s390: Convert call_rcu() to kfree_rcu(), drop ext_int_hash_update()

The call_rcu() in unregister_external_interrupt() invokes
ext_int_hash_update(), which just does a kfree().  Convert the
call_rcu() to kfree_rcu(), allowing ext_int_hash_update() to
be eliminated.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/kernel/irq.c

@@ -165,13 +165,6 @@ static inline int ext_hash(u16 code)
 	return (code + (code >> 9)) & 0xff;
 }
 
-static void ext_int_hash_update(struct rcu_head *head)
-{
-	struct ext_int_info *p = container_of(head, struct ext_int_info, rcu);
-
-	kfree(p);
-}
-
 int register_external_interrupt(u16 code, ext_int_handler_t handler)
 {
 	struct ext_int_info *p;
@@ -202,7 +195,7 @@ int unregister_external_interrupt(u16 code, ext_int_handler_t handler)
 	list_for_each_entry_rcu(p, &ext_int_hash[index], entry)
 		if (p->code == code && p->handler == handler) {
 			list_del_rcu(&p->entry);
-			call_rcu(&p->rcu, ext_int_hash_update);
+			kfree_rcu(p, rcu);
 		}
 	spin_unlock_irqrestore(&ext_int_hash_lock, flags);
 	return 0;