Remove compile warning from net/ipv4/netfilter/ip_nat_helper.c

diff -Nru a/net/ipv4/netfilter/ip_nat_helper.c b/net/ipv4/netfilter/ip_nat_helper.c
@@ -84,7 +84,6 @@
 	iph = (*skb)->nh.iph;
 	if (iph->protocol == IPPROTO_TCP) {
 		struct tcphdr *tcph = (void *)iph + iph->ihl*4;
-		void *data = (void *)tcph + tcph->doff*4;
 
 		DEBUGP("ip_nat_resize_packet: Seq_offset before: ");
 		DUMP_OFFSET(this_way);