ubifs: Fix double unlock around orphan_delete()

commit 4dd75b33 upstream.

We unlock after orphan_delete(), so no need to unlock
in the function too.

Reported-by: Han Xu <han.xu@nxp.com>
Fixes: 8009ce95 ("ubifs: Don't leak orphans on memory during commit")
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>