pgtable: fix s390 ptdesc field comments

pgtable: fix s390 ptdesc field comments

Patch series "minor ptdesc updates", v3.

This patch (of 2):

Since commit d08d4e7cd6bf ("s390/mm: use full 4KB page for 2KB PTE") there
is no fragmented page tracking on s390.  Fix the corresponding comments.

Link: https://lkml.kernel.org/r/cover.1700594815.git.agordeev@linux.ibm.com
Link: https://lkml.kernel.org/r/2eead241f3a45bed26c7911cf66bded1e35670b8.1700594815.git.agordeev@linux.ibm.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>