avcodec/dcadec: set AV_CLASS_CATEGORY

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dcadec.c

@@ -2615,6 +2615,7 @@ static const AVClass dca_decoder_class = {
     .item_name  = av_default_item_name,
     .option     = options,
     .version    = LIBAVUTIL_VERSION_INT,
+    .category   = AV_CLASS_CATEGORY_DECODER,
 };
 
 AVCodec ff_dca_decoder = {