[media] uvcvideo: annotate a switch fall through

Without annotations, gcc 7.1 will complain.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/uvc/uvc_video.c

@@ -1323,7 +1323,7 @@ static void uvc_video_complete(struct urb *urb)
 	default:
 		uvc_printk(KERN_WARNING, "Non-zero status (%d) in video "
 			"completion handler.\n", urb->status);
-
+		/* fall through */
 	case -ENOENT:		/* usb_kill_urb() called. */
 		if (stream->frozen)
 			return;