s390: use pfn_swap_entry_folio() in ptep_zap_swap_entry()

Call pfn_swap_entry_folio() in ptep_zap_swap_entry() as preparation for
converting mm counter functions to take a folio.

Link: https://lkml.kernel.org/r/20240111152429.3374566-5-willy@infradead.org


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>