avcodec/h261dec: Remove nonsense information from error message

The "invalid mtype index" here is always -1, because that is
the value the VLC api uses for not existent leafs in an incomplete tree.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/h261dec.c

@@ -415,8 +415,7 @@ static int h261_decode_mb(H261DecContext *h)
     // Read mtype
     com->mtype = get_vlc2(&s->gb, h261_mtype_vlc, H261_MTYPE_VLC_BITS, 2);
     if (com->mtype < 0) {
-        av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index %d\n",
-               com->mtype);
+        av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index\n");
         return SLICE_ERROR;
     }