Fix pkt->pos to really point at start of packet for mtv audio packets.

Originally committed as revision 14019 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mtv.c

@@ -148,6 +148,7 @@ static int mtv_read_packet(AVFormatContext *s, AVPacket *pkt)
             return AVERROR(EIO);
 
         mtv->audio_packet_count++;
+        pkt->pos -= MTV_AUDIO_PADDING_SIZE;
         pkt->stream_index = AUDIO_SID;
 
     }else