ip: fix warning in xfrm4_mode_tunnel_input

Same problem as IPv6

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/xfrm4_mode_tunnel.c b/net/ipv4/xfrm4_mode_tunnel.c
index 1162ace..fe5189e 100644
--- a/net/ipv4/xfrm4_mode_tunnel.c
+++ b/net/ipv4/xfrm4_mode_tunnel.c
@@ -142,7 +142,8 @@
 	for_each_input_rcu(rcv_notify_handlers, handler)
 		handler->handler(skb);
 
-	if (err = skb_unclone(skb, GFP_ATOMIC))
+	err = skb_unclone(skb, GFP_ATOMIC);
+	if (err)
 		goto out;
 
 	if (x->props.flags & XFRM_STATE_DECAP_DSCP)