[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_tftp.c b/net/ipv4/netfilter/nf_nat_tftp.c
index 0ecec70..1360a94 100644
--- a/net/ipv4/netfilter/nf_nat_tftp.c
+++ b/net/ipv4/netfilter/nf_nat_tftp.c
@@ -43,7 +43,7 @@
 
 static int __init nf_nat_tftp_init(void)
 {
-	BUG_ON(rcu_dereference(nf_nat_tftp_hook));
+	BUG_ON(nf_nat_tftp_hook != NULL);
 	rcu_assign_pointer(nf_nat_tftp_hook, help);
 	return 0;
 }