asfdec: add side data to ASFStream packet instead of output packet.

fixes memleak of side data

libavformat/asfdec.c

@@ -979,7 +979,7 @@ static int ff_asf_parse_packet(AVFormatContext *s, AVIOContext *pb, AVPacket *pk
             asf_st->packet_pos= asf->packet_pos;
             if (asf_st->pkt.data && asf_st->palette_changed) {
                 uint8_t *pal;
-                pal = av_packet_new_side_data(pkt, AV_PKT_DATA_PALETTE,
+                pal = av_packet_new_side_data(&asf_st->pkt, AV_PKT_DATA_PALETTE,
                                               AVPALETTE_SIZE);
                 if (!pal) {
                     av_log(s, AV_LOG_ERROR, "Cannot append palette to packet\n");