[NETFILTER]: remove unneeded rcu_dereference() calls

As noticed by Paul McKenney, the rcu_dereference calls in the init path
of NAT modules are unneeded, remove them.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/netfilter/nf_nat_sip.c b/net/ipv4/netfilter/nf_nat_sip.c
index ce9edbc..3ca9897 100644
--- a/net/ipv4/netfilter/nf_nat_sip.c
+++ b/net/ipv4/netfilter/nf_nat_sip.c
@@ -293,8 +293,8 @@
 
 static int __init nf_nat_sip_init(void)
 {
-	BUG_ON(rcu_dereference(nf_nat_sip_hook));
-	BUG_ON(rcu_dereference(nf_nat_sdp_hook));
+	BUG_ON(nf_nat_sip_hook != NULL);
+	BUG_ON(nf_nat_sdp_hook != NULL);
 	rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
 	rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp);
 	return 0;