mm: replace READ_ONCE() in pud_trans_unstable()

mm: replace READ_ONCE() in pud_trans_unstable()

Replace READ_ONCE() with the existing standard page table accessor for PUD
aka pudp_get() in pud_trans_unstable().  This does not create any
functional change for platforms that do not override pudp_get(), which
still defaults to READ_ONCE().

Link: https://lkml.kernel.org/r/20260227040300.2091901-1-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>