vc1dec: use codec_id instead of codec_tag for VC1IMAGE

the rest of the code is using codec_id everywhere already
Signed-off-by: Vladimir Pantelic <vladoman@gmail.com>
Signed-off-by: Kostya Shishkov <kostya.shishkov@gmail.com>

libavcodec/vc1dec.c

@@ -5231,7 +5231,7 @@ static av_cold int vc1_decode_init(AVCodecContext *avctx)
             av_log(avctx, AV_LOG_ERROR, "Incomplete extradata\n");
             return -1;
         }
-        v->res_sprite = (avctx->codec_tag == MKTAG('W','V','P','2'));
+        v->res_sprite = (avctx->codec_id == AV_CODEC_ID_VC1IMAGE);
     }
 
     avctx->profile = v->profile;