avcodec/utvideodec: fix use of get_vlc2()

The max depth is 3
Found-by: Christophe Gisquet <christophe.gisquet@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/utvideodec.c

@@ -155,7 +155,7 @@ static int decode_plane(UtvideoContext *c, int plane_no,
                            "Slice decoding ran out of bits\n");
                     goto fail;
                 }
-                pix = get_vlc2(&gb, vlc.table, vlc.bits, 4);
+                pix = get_vlc2(&gb, vlc.table, vlc.bits, 3);
                 if (pix < 0) {
                     av_log(c->avctx, AV_LOG_ERROR, "Decoding error\n");
                     goto fail;