tcm_fc: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

The use of "rcu_assign_pointer()" is NULLing out the pointer.
According to RCU_INIT_POINTER()'s block comment:
"1.   This use of RCU_INIT_POINTER() is NULLing out the pointer"
it is better to use it instead of rcu_assign_pointer() because it has a
smaller overhead.

The following Coccinelle semantic patch was used:
@@
@@

- rcu_assign_pointer
+ RCU_INIT_POINTER
  (..., NULL)
Signed-off-by: NAndreea-Cristina Bernat <bernat.ada@gmail.com>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>

drivers/target/tcm_fc/tfc_sess.c

@@ -98,7 +98,7 @@ static void ft_tport_delete(struct ft_tport *tport)
 	ft_sess_delete_all(tport);
 	lport = tport->lport;
 	BUG_ON(tport != lport->prov[FC_TYPE_FCP]);
-	rcu_assign_pointer(lport->prov[FC_TYPE_FCP], NULL);
+	RCU_INIT_POINTER(lport->prov[FC_TYPE_FCP], NULL);
 
 	tpg = tport->tpg;
 	if (tpg) {