gre: remove duplicated assignment of iph

iph is being assigned the same value twice; remove the redundant
first assignment. (Thanks to Nikolay Aleksandrov for pointing out
that the first asssignment should be removed and not the second)

Fixes warning:
net/ipv4/ip_gre.c:265:2: warning: Value stored to 'iph' is never read
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -262,7 +262,6 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	int len;
 
 	itn = net_generic(net, erspan_net_id);
-	iph = ip_hdr(skb);
 	len = gre_hdr_len + sizeof(*ershdr);
 
 	if (unlikely(!pskb_may_pull(skb, len)))