vcgencmd: Avoid compiler complaints

In file included from /usr/include/string.h:535,
                 from /<<PKGBUILDDIR>>/vcgencmd/vcgencmd.c:34:
In function ‘strncat’,
    inlined from ‘gencmd’ at /<<PKGBUILDDIR>>/vcgencmd/vcgencmd.c:109:4,
    inlined from ‘main’ at /<<PKGBUILDDIR>>/vcgencmd/vcgencmd.c:152:14:
/usr/include/arm-linux-gnueabihf/bits/string_fortified.h:138:10: warning: ‘__builtin___strncat_chk’ specified bound 1024 equals destination size [-Wstringop-overflow=]
  138 |   return __builtin___strncat_chk (__dest, __src, __len,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  139 |                                   __glibc_objsize (__dest));
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~

can be seen with "gcc -O2 -Wall"

Author: popcornmix

vcgencmd/vcgencmd.c

@@ -105,8 +105,8 @@ static unsigned gencmd(int file_desc, const char *command, char *result, int res
    p[0] = i*sizeof *p; // actual size
 
    mbox_property(file_desc, p);
-   result[0] = 0;
-   strncat(result, (const char *)(p+6), result_len);
+   memcpy(result, p+6, result_len);
+   result[result_len -1] = '\0';
 
    return p[5];
 }