avformat/asfdec_o: Don't reset twice

A variable has been assigned a value twice consecutively; essentially
the same happens when one performs av_init_packet on an AVPacket after
a call to av_packet_unref.

Found via PVS-Studio (see ticket #8156).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/asfdec_o.c

@@ -1135,9 +1135,7 @@ static void reset_packet(ASFPacket *asf_pkt)
     asf_pkt->duration  = 0;
     asf_pkt->flags     = 0;
     asf_pkt->dts       = 0;
-    asf_pkt->duration  = 0;
     av_packet_unref(&asf_pkt->avpkt);
-    av_init_packet(&asf_pkt->avpkt);
 }
 
 static int asf_read_replicated_data(AVFormatContext *s, ASFPacket *asf_pkt)