netfilter: nf_conntrack: remove double assignment

The protonet pointer will unconditionally be rewritten, so just do the
needed assignment first.
Signed-off-by: Aaron Conole <aconole@bytheb.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_proto.c

@@ -441,9 +441,8 @@ EXPORT_SYMBOL_GPL(nf_ct_l4proto_unregister_one);
 void nf_ct_l4proto_pernet_unregister_one(struct net *net,
 					 struct nf_conntrack_l4proto *l4proto)
 {
-	struct nf_proto_net *pn = NULL;
+	struct nf_proto_net *pn = nf_ct_l4proto_net(net, l4proto);
 
-	pn = nf_ct_l4proto_net(net, l4proto);
 	if (pn == NULL)
 		return;