btrfs: make close_ctree return void

There's no user of the return value and we can get rid of the comment in
put_super.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 354cc3f..ec32bea 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3623,7 +3623,7 @@
 	return btrfs_commit_transaction(trans, root);
 }
 
-int close_ctree(struct btrfs_root *root)
+void close_ctree(struct btrfs_root *root)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	int ret;
@@ -3711,8 +3711,6 @@
 
 	btrfs_free_block_rsv(root, root->orphan_block_rsv);
 	root->orphan_block_rsv = NULL;
-
-	return 0;
 }
 
 int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,