esp4: remove assignment in if condition

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/esp4.c

@@ -392,8 +392,10 @@ static int esp_input(struct xfrm_state *x, struct sk_buff *skb)
 	if (elen <= 0)
 		goto out;
 
-	if ((err = skb_cow_data(skb, 0, &trailer)) < 0)
+	err = skb_cow_data(skb, 0, &trailer);
+	if (err < 0)
 		goto out;
+
 	nfrags = err;
 
 	assoclen = sizeof(*esph);