libvo-amrwbenc: Add braces to shut up gcc warning.

libavcodec/libvo-amrwbenc.c:37:5: warning: missing braces around initializer

libavcodec/libvo-amrwbenc.c

@@ -34,7 +34,7 @@ typedef struct AMRWBContext {
 } AMRWBContext;
 
 static const AVOption options[] = {
-    { "dtx", "Allow DTX (generate comfort noise)", offsetof(AMRWBContext, allow_dtx), FF_OPT_TYPE_INT, 0, 0, 1, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
+    { "dtx", "Allow DTX (generate comfort noise)", offsetof(AMRWBContext, allow_dtx), FF_OPT_TYPE_INT, { 0 }, 0, 1, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
     { NULL }
 };