oic: device_id string was leaking

As device_id is a fixed size string, we don't even need to allocate it
in the heap

One way to check this bahaviour is running the light-server +
light-scan/light-client-scan sample located in src/samples/flow/oic/.
Use client scan to connect to different servers. Do it several times.
After that closes the client.

Leak information from compiler sanitizer:

Direct leak of 64 byte(s) in 4 object(s) allocated from:
    #0 0x7fd5bbecf93a in __interceptor_malloc /build/gcc-multilib/src/gcc-5.2.0/libsanitizer/asan/asan_malloc_linux.cc:38
    #1 0x7fd59dfa0a29 in hex_ascii_to_binary (//home/otavio/local/soletta/lib/soletta/modules//flow//oic.so+0x8a29)
    #2 0x7fd59dfa0bed in client_connect (//home/otavio/local/soletta/lib/soletta/modules//flow//oic.so+0x8bed)
    #3 0x7fd59dfa32df in device_id_process (//home/otavio/local/soletta/lib/soletta/modules//flow//oic.so+0xb2df)
    #4 0x7fd5bb51b2ca in dispatch_process (/home/otavio/local/soletta/lib/libsoletta.so.0+0x1a42ca)
    #5 0x7fd5bb51d282 in flow_send_do (/home/otavio/local/soletta/lib/libsoletta.so.0+0x1a6282)
    #6 0x7fd5bb51d7e1 in flow_send_idle (/home/otavio/local/soletta/lib/libsoletta.so.0+0x1a67e1)
    #7 0x7fd5bb494a46 in sol_mainloop_common_timeout_process (/home/otavio/local/soletta/lib/libsoletta.so.0+0x11da46)
    #8 0x7fd5bb499244 in sol_mainloop_impl_iter (/home/otavio/local/soletta/lib/libsoletta.so.0+0x122244)
    #9 0x7fd5bb496022 in sol_mainloop_impl_run (/home/otavio/local/soletta/lib/libsoletta.so.0+0x11f022)
    #10 0x7fd5bb499b74 in sol_run (/home/otavio/local/soletta/lib/libsoletta.so.0+0x122b74)
    #11 0x403a7a in main (/home/otavio/local/soletta/bin/sol-fbp-runner+0x403a7a)
    #12 0x7fd5b7df360f in __libc_start_main (/usr/lib/libc.so.6+0x2060f)

Direct leak of 16 byte(s) in 1 object(s) allocated from:
    #0 0x7fd5bbecf93a in __interceptor_malloc /build/gcc-multilib/src/gcc-5.2.0/libsanitizer/asan/asan_malloc_linux.cc:38
    #1 0x7fd59dfa0a29 in hex_ascii_to_binary (//home/otavio/local/soletta/lib/soletta/modules//flow//oic.so+0x8a29)
    #2 0x7fd59dfa0bed in client_connect (//home/otavio/local/soletta/lib/soletta/modules//flow//oic.so+0x8bed)
    #3 0x7fd59dfa32df in device_id_process (//home/otavio/local/soletta/lib/soletta/modules//flow//oic.so+0xb2df)
    #4 0x7fd5bb51b2ca in dispatch_process (/home/otavio/local/soletta/lib/libsoletta.so.0+0x1a42ca)
    #5 0x7fd5bb51d282 in flow_send_do (/home/otavio/local/soletta/lib/libsoletta.so.0+0x1a6282)
    #6 0x7fd5bb51d7e1 in flow_send_idle (/home/otavio/local/soletta/lib/libsoletta.so.0+0x1a67e1)
    #7 0x7fd5bb494a46 in sol_mainloop_common_timeout_process (/home/otavio/local/soletta/lib/libsoletta.so.0+0x11da46)
    #8 0x7fd5bb494e13 in sol_mainloop_common_idler_process (/home/otavio/local/soletta/lib/libsoletta.so.0+0x11de13)
    #9 0x7fd5bb499258 in sol_mainloop_impl_iter (/home/otavio/local/soletta/lib/libsoletta.so.0+0x122258)
    #10 0x7fd5bb496022 in sol_mainloop_impl_run (/home/otavio/local/soletta/lib/libsoletta.so.0+0x11f022)
    #11 0x7fd5bb499b74 in sol_run (/home/otavio/local/soletta/lib/libsoletta.so.0+0x122b74)
    #12 0x403a7a in main (/home/otavio/local/soletta/bin/sol-fbp-runner+0x403a7a)
    #13 0x7fd5b7df360f in __libc_start_main (/usr/lib/libc.so.6+0x2060f)

Signed-off-by: Otavio Pontes <otavio.pontes@intel.com>

data/scripts/sol-oic-gen.py

@@ -1030,7 +1030,7 @@ def master_c_as_string(generated, oic_gen_c, oic_gen_h):
     struct sol_oic_client client;
 
     const char *rt;
-    char *device_id;
+    char device_id[DEVICE_ID_LEN];
     struct sol_ptr_vector scanned_ids;
 };
 
@@ -1416,20 +1416,14 @@ def master_c_as_string(generated, oic_gen_c, oic_gen_h):
     return 0;
 }
 
-static char *
-hex_ascii_to_binary(const char *ascii)
+static void
+hex_ascii_to_binary(const char *ascii, char *binary)
 {
-    char *binary = malloc(DEVICE_ID_LEN);
-
-    if (likely(binary)) {
-        const char *p;
-        size_t i;
-
-        for (p = ascii, i = 0; i < DEVICE_ID_LEN; i++, p += 2)
-            binary[i] = as_nibble(*p) << 4 | as_nibble(*(p + 1));
-    }
+    const char *p;
+    size_t i;
 
-    return binary;
+    for (p = ascii, i = 0; i < DEVICE_ID_LEN; i++, p += 2)
+        binary[i] = as_nibble(*p) << 4 | as_nibble(*(p + 1));
 }
 
 static int
@@ -1440,7 +1434,7 @@ def master_c_as_string(generated, oic_gen_c, oic_gen_h):
         return 0;
     }
 
-    resource->device_id = hex_ascii_to_binary(device_id);
+    hex_ascii_to_binary(device_id, resource->device_id);
     SOL_NULL_CHECK(resource->device_id, -ENOMEM);
 
     if (resource->find_timeout)
@@ -1497,7 +1491,6 @@ def master_c_as_string(generated, oic_gen_c, oic_gen_h):
     sol_ptr_vector_init(&resource->scanned_ids);
     resource->node = node;
     resource->find_timeout = NULL;
-    resource->device_id = NULL;
     resource->update_schedule_timeout = NULL;
     resource->resource = NULL;
     resource->funcs = funcs;
@@ -1513,8 +1506,6 @@ def master_c_as_string(generated, oic_gen_c, oic_gen_h):
 static void
 client_resource_close(struct client_resource *resource)
 {
-    free(resource->device_id);
-
     if (resource->find_timeout)
         sol_timeout_del(resource->find_timeout);
     if (resource->update_schedule_timeout)