mm/debug_vm_pgtable: replace WRITE_ONCE() with pxd_clear()

mm/debug_vm_pgtable: replace WRITE_ONCE() with pxd_clear()

Replace WRITE_ONCE() with generic pxd_clear() to clear out the page table
entries as required.  Besides this does not cause any functional change as
well.

Link: https://lkml.kernel.org/r/20260227061204.2215395-1-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Suggested-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Ackeed-by: SeongJae Park <sj@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>