matroskadec: use correct compression parameters for current track CodecPrivate

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/matroskadec.c

@@ -1455,7 +1455,7 @@ static int matroska_read_header(AVFormatContext *s)
     for (i=0; i < matroska->tracks.nb_elem; i++) {
         MatroskaTrack *track = &tracks[i];
         enum AVCodecID codec_id = AV_CODEC_ID_NONE;
-        EbmlList *encodings_list = &tracks->encodings;
+        EbmlList *encodings_list = &track->encodings;
         MatroskaTrackEncoding *encodings = encodings_list->elem;
         uint8_t *extradata = NULL;
         int extradata_size = 0;