Btrfs: add __init macro to btrfs init functions

Adding __init macro gives kernel a hint that this function is only used
during the initialization phase and its memory resources can be freed up
after.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2bab93f..c8a3e84 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9569,7 +9569,7 @@ void btrfs_destroy_cachep(void)
 	kmem_cache_destroy(btrfs_free_space_cachep);
 }
 
-int btrfs_init_cachep(void)
+int __init btrfs_init_cachep(void)
 {
 	btrfs_inode_cachep = kmem_cache_create("btrfs_inode",
 			sizeof(struct btrfs_inode), 0,