mm/mm_init.c: use hotplug_memory_notifier() directly

Since patch 3163462 has already updated the minimum gcc version to 5.1.
The previous problem mentioned in patch f02c696 is not existed. So we
can now revert to use hotplug_memory_notifier() directly rather than
register_hotmemory_notifier().

Signed-off-by: Liu Shixin <liushixin2@huawei.com>

mm/mm_init.c

@@ -178,16 +178,10 @@ static int __meminit mm_compute_batch_notifier(struct notifier_block *self,
 	return NOTIFY_OK;
 }
 
-static struct notifier_block compute_batch_nb __meminitdata = {
-	.notifier_call = mm_compute_batch_notifier,
-	.priority = IPC_CALLBACK_PRI, /* use lowest priority */
-};
-
 static int __init mm_compute_batch_init(void)
 {
 	mm_compute_batch(sysctl_overcommit_memory);
-	register_hotmemory_notifier(&compute_batch_nb);
-
+	hotplug_memory_notifier(&mm_compute_batch_notifier, IPC_CALLBACK_PRI);
 	return 0;
 }