virtio-lib: break waiting for reset completion if the device not present

https://bugzilla.redhat.com/show_bug.cgi?id=1924998

If the physical device was removed it is possible that we'll
enter endless loop as the device status will never return 0.
Break the loop if the PCI config space is not readable at
offset 0 (vendor ID).

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>

VirtIO/VirtIOPCIModern.c

@@ -184,6 +184,11 @@ static void vio_modern_reset(VirtIODevice *vdev)
      * including MSI-X interrupts, if any.
      */
     while (ioread8(vdev, &vdev->common->device_status)) {
+        u16 val;
+        if (pci_read_config_word(vdev, 0, &val) || val == 0xffff) {
+            DPrintf(0, ("PCI config space is not readable, probably the device is removed\n"));
+            break;
+        }
         vdev_sleep(vdev, 1);
     }
 }