libavcodec/utils: Add braces to shut up gcc warnings

libavcodec/utils.c:1050:5: warning: missing braces around initializer [-Wmissing-braces]
libavcodec/utils.c:1314:5: warning: missing braces around initializer [-Wmissing-braces]

libavcodec/utils.c

@@ -1047,7 +1047,7 @@ int attribute_align_arg avcodec_encode_audio(AVCodecContext *avctx,
                                              const short *samples)
 {
     AVPacket pkt;
-    AVFrame frame0 = { 0 };
+    AVFrame frame0 = { { 0 } };
     AVFrame *frame;
     int ret, samples_size, got_packet;
 
@@ -1311,7 +1311,7 @@ int attribute_align_arg avcodec_decode_audio3(AVCodecContext *avctx, int16_t *sa
                                               int *frame_size_ptr,
                                               AVPacket *avpkt)
 {
-    AVFrame frame = {0};
+    AVFrame frame = { { 0 } };
     int ret, got_frame = 0;
 
     if (avctx->get_buffer != avcodec_default_get_buffer) {