btrfs: reserve no transaction units in btrfs_ioctl_set_features

Added in patch "btrfs: add ioctls to query/change feature bits online"
modifications to superblock don't need to reserve metadata blocks when
starting a transaction.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 5bbf6b7..ebdd866 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4690,7 +4690,7 @@
 	if (ret)
 		return ret;
 
-	trans = btrfs_start_transaction(root, 1);
+	trans = btrfs_start_transaction(root, 0);
 	if (IS_ERR(trans))
 		return PTR_ERR(trans);