avformat/matroskadec: fix the type of the TrackLanguage

It's an ASCII string, not a UTF-8 string.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/matroskadec.c

@@ -554,7 +554,7 @@ static EbmlSyntax matroska_track[] = {
     { MATROSKA_ID_CODECID,               EBML_STR,   0, offsetof(MatroskaTrack, codec_id) },
     { MATROSKA_ID_CODECPRIVATE,          EBML_BIN,   0, offsetof(MatroskaTrack, codec_priv) },
     { MATROSKA_ID_CODECDELAY,            EBML_UINT,  0, offsetof(MatroskaTrack, codec_delay) },
-    { MATROSKA_ID_TRACKLANGUAGE,         EBML_UTF8,  0, offsetof(MatroskaTrack, language),     { .s = "eng" } },
+    { MATROSKA_ID_TRACKLANGUAGE,         EBML_STR,   0, offsetof(MatroskaTrack, language),     { .s = "eng" } },
     { MATROSKA_ID_TRACKDEFAULTDURATION,  EBML_UINT,  0, offsetof(MatroskaTrack, default_duration) },
     { MATROSKA_ID_TRACKTIMECODESCALE,    EBML_FLOAT, 0, offsetof(MatroskaTrack, time_scale),   { .f = 1.0 } },
     { MATROSKA_ID_TRACKFLAGDEFAULT,      EBML_UINT,  0, offsetof(MatroskaTrack, flag_default), { .u = 1 } },