ubifs: Fix ubifs_tnc_lookup() usage in do_kill_orphans()

commit 4ab25ac8 upstream.

Orphans are allowed to point to deleted inodes.
So -ENOENT is not a fatal error.

Reported-by: Кочетков Максим <fido_max@inbox.ru>
Reported-and-tested-by: "Christian Berger" <Christian.Berger@de.bosch.com>
Tested-by: Karl Olsen <karl@micro-technic.com>
Tested-by: Jef Driesen <jef.driesen@niko.eu>
Fixes: ee1438ce ("ubifs: Check link count of inodes when killing orphans.")
Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: Christian Eggers <ceggers@arri.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>