Revert "ubifs: xattr: Don't operate on deleted inodes"

This reverts commit 11a6fc3d.
UBIFS wants to assert that xattr operations are only issued on files
with positive link count. The said patch made this operations return
-ENOENT for unlinked files such that the asserts will no longer trigger.
This was wrong since xattr operations are perfectly fine on unlinked
files.
Instead the assertions need to be fixed/removed.

Cc: <stable@vger.kernel.org>
Fixes: 11a6fc3d ("ubifs: xattr: Don't operate on deleted inodes")
Reported-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Richard Weinberger <richard@nod.at>