btrfs: add (the only possible) __exit annotation

Recently, the __init annotations have been added. There's unfortunatelly
only one case where we can add __exit, because most of the cleanup
helpers are also called from the __init phase.

As the __exit annotated functions get discarded completely for a
built-in code, we'd miss them from the init phase.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -279,7 +279,7 @@ static void btrfs_kobject_uevent(struct block_device *bdev,
 			&disk_to_dev(bdev->bd_disk)->kobj);
 }
 
-void btrfs_cleanup_fs_uuids(void)
+void __exit btrfs_cleanup_fs_uuids(void)
 {
 	struct btrfs_fs_devices *fs_devices;
 

fs/btrfs/volumes.h

@@ -436,7 +436,7 @@ struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
 					const u8 *uuid);
 int btrfs_rm_device(struct btrfs_fs_info *fs_info,
 		    const char *device_path, u64 devid);
-void btrfs_cleanup_fs_uuids(void);
+void __exit btrfs_cleanup_fs_uuids(void);
 int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len);
 int btrfs_grow_device(struct btrfs_trans_handle *trans,
 		      struct btrfs_device *device, u64 new_size);