Btrfs: don't flush all delalloc inodes when we doesn't get s_umount lock

We needn't flush all delalloc inodes when we doesn't get s_umount lock,
or we would make the tasks wait for a long time.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index ec1c3f3..9f22905 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -491,7 +491,7 @@
 	 * flush all outstanding I/O and inode extent mappings before the
 	 * copy operation is declared as being finished
 	 */
-	ret = btrfs_start_delalloc_roots(root->fs_info, 0);
+	ret = btrfs_start_delalloc_roots(root->fs_info, 0, -1);
 	if (ret) {
 		mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
 		return ret;