Btrfs: do not check inode's runtime flags under root->orphan_lock

It's not necessary to hold ->orphan_lock when checking inode's runtime
flags.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>