rcu: convert uses of rcu_assign_pointer(x, NULL) to RCU_INIT_POINTER

When assigning a NULL value to an RCU protected pointer, no barrier
is needed. The rcu_assign_pointer, used to handle that but will soon
change to not handle the special case.

Convert all rcu_assign_pointer of NULL value.

//smpl
@@ expression P; @@

- rcu_assign_pointer(P, NULL)
+ RCU_INIT_POINTER(P, NULL)

// </smpl>

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/netfilter/nf_nat_amanda.c b/net/ipv4/netfilter/nf_nat_amanda.c
index 703f366f..7b22382 100644
--- a/net/ipv4/netfilter/nf_nat_amanda.c
+++ b/net/ipv4/netfilter/nf_nat_amanda.c
@@ -70,14 +70,14 @@
 
 static void __exit nf_nat_amanda_fini(void)
 {
-	rcu_assign_pointer(nf_nat_amanda_hook, NULL);
+	RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
 	synchronize_rcu();
 }
 
 static int __init nf_nat_amanda_init(void)
 {
 	BUG_ON(nf_nat_amanda_hook != NULL);
-	rcu_assign_pointer(nf_nat_amanda_hook, help);
+	RCU_INIT_POINTER(nf_nat_amanda_hook, help);
 	return 0;
 }