ubifs: Fix RENAME_WHITEOUT support

Remove faulty leftover check in do_rename(), apparently introduced in a
merge that combined whiteout support changes with commit f03b8ad8
("fs: support RENAME_NOREPLACE for local filesystems")

Fixes: f03b8ad8 ("fs: support RENAME_NOREPLACE for local
filesystems")
Fixes: 9e0a1fff

 ("ubifs: Implement RENAME_WHITEOUT")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Richard Weinberger <richard@nod.at>