net: Remove useless local var pkt

This has been pointless since commit 605d52e62, which was a
search-and-replace, overlooked the redundancy.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/net_rx_pkt.c

@@ -159,7 +159,6 @@ void net_rx_pkt_attach_iovec_ex(struct NetRxPkt *pkt,
 void net_rx_pkt_dump(struct NetRxPkt *pkt)
 {
 #ifdef NET_RX_PKT_DEBUG
-    NetRxPkt *pkt = (NetRxPkt *)pkt;
     assert(pkt);
 
     printf("RX PKT: tot_len: %d, vlan_stripped: %d, vlan_tag: %d\n",