geneve: testing the wrong variable in geneve6_build_skb()

We intended to test "err" and not "skb".

Fixes: aed069df099c ('ip_tunnel_core: iptunnel_handle_offloads returns int and doesn't free skb')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/geneve.c

@@ -733,7 +733,7 @@ static int geneve6_build_skb(struct dst_entry *dst, struct sk_buff *skb,
 		goto free_dst;
 
 	err = udp_tunnel_handle_offloads(skb, udp_sum);
-	if (IS_ERR(skb))
+	if (err)
 		goto free_dst;
 
 	gnvh = (struct genevehdr *)__skb_push(skb, sizeof(*gnvh) + opt_len);