avcodec/mpeg12dec: flush a53 data

Signed-off-by: Aman Karmani <aman@tmm1.net>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/mpeg12dec.c

@@ -2862,6 +2862,7 @@ static void flush(AVCodecContext *avctx)
     s->sync       = 0;
     s->closed_gop = 0;
 
+    av_buffer_unref(&s->a53_buf_ref);
     ff_mpeg_flush(avctx);
 }