avcodec/msmpeg4dec: Correct table depth

Fixes undefined shift
Fixes: 1381/clusterfuzz-testcase-minimized-5513944540119040

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/msmpeg4dec.c

@@ -140,7 +140,7 @@ static int msmpeg4v12_decode_mb(MpegEncContext *s, int16_t block[6][64])
         if(s->msmpeg4_version==2)
             cbp= get_vlc2(&s->gb, v2_intra_cbpc_vlc.table, V2_INTRA_CBPC_VLC_BITS, 1);
         else
-            cbp= get_vlc2(&s->gb, ff_h263_intra_MCBPC_vlc.table, INTRA_MCBPC_VLC_BITS, 1);
+            cbp= get_vlc2(&s->gb, ff_h263_intra_MCBPC_vlc.table, INTRA_MCBPC_VLC_BITS, 2);
         if(cbp<0 || cbp>3){
             av_log(s->avctx, AV_LOG_ERROR, "cbpc %d invalid at %d %d\n", cbp, s->mb_x, s->mb_y);
             return -1;