ipv4: netfilter: use PTR_RET instead of IS_ERR + PTR_ERR

This uses PTR_RET instead of IS_ERR and PTR_ERR in order to increase
readability.
Signed-off-by: Silviu-Mihai Popescu <silviupopescu1990@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/arptable_filter.c

@@ -48,9 +48,7 @@ static int __net_init arptable_filter_net_init(struct net *net)
 	net->ipv4.arptable_filter =
 		arpt_register_table(net, &packet_filter, repl);
 	kfree(repl);
-	if (IS_ERR(net->ipv4.arptable_filter))
-		return PTR_ERR(net->ipv4.arptable_filter);
-	return 0;
+	return PTR_RET(net->ipv4.arptable_filter);
 }
 
 static void __net_exit arptable_filter_net_exit(struct net *net)