netfilter: ctnetlink: fix error return code in init path

Initialize return variable before exiting on an error path.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
(
if@p1 (\(ret < 0\|ret != 0\))
{ ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
when != &ret
*if(...)
{
... when != ret = e2
when forall
return ret;
}

// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_conntrack_netlink.c

···
 		goto err_unreg_subsys;
 	}
 
-	if (register_pernet_subsys(&ctnetlink_net_ops)) {
+	ret = register_pernet_subsys(&ctnetlink_net_ops);
+	if (ret < 0) {
 		pr_err("ctnetlink_init: cannot register pernet operations\n");
 		goto err_unreg_exp_subsys;
 	}