aoe: add __exit annotation

Add __exit annotation to cleanup helper which
is only called once in the module.
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/aoe/aoemain.c

@@ -24,7 +24,7 @@ static void discover_timer(struct timer_list *t)
 	aoecmd_cfg(0xffff, 0xff);
 }
 
-static void
+static void __exit
 aoe_exit(void)
 {
 	del_timer_sync(&timer);