revert "squashfs: harden sanity check in squashfs_read_xattr_id_table"

This fix was nacked by Philip, for reasons identified in the email linked
below.

Link: https://lkml.kernel.org/r/68f15d67-8945-2728-1f17-5b53a80ec52d@squashfs.org.uk
Fixes: 72e544b1

 ("squashfs: harden sanity check in squashfs_read_xattr_id_table")
Cc: Alexey Khoroshilov <khoroshilov@ispras.ru>
Cc: Fedor Pchelkin <pchelkin@ispras.ru>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>