btrfs: only dirty the inode in btrfs_update_time if something was changed
At this point, we know that "now" and the file times may differ, and we
suspect that the i_version has been flagged to be bumped. Attempt to
bump the i_version, and only mark the inode dirty if that actually
occurred or if one of the times was updated.
Signed-off-by: Jeff Layton <jlayton@redhat.com> Acked-by: David Sterba <dsterba@suse.com> Reviewed-by: Liu Bo <bo.li.liu@oracle.com>