mm: use pfn_swap_entry_folio() in __split_huge_pmd_locked()

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

Link: https://lkml.kernel.org/r/20240111152429.3374566-6-willy@infradead.orgSigned-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>

mm/huge_memory.c

@@ -2442,7 +2442,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 			swp_entry_t entry;
 
 			entry = pmd_to_swp_entry(old_pmd);
-			page = pfn_swap_entry_to_page(entry);
+			folio = pfn_swap_entry_folio(entry);
 		} else {
 			page = pmd_page(old_pmd);
 			folio = page_folio(page);
@@ -2453,7 +2453,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 			folio_remove_rmap_pmd(folio, page, vma);
 			folio_put(folio);
 		}
-		add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
+		add_mm_counter(mm, mm_counter_file(&folio->page), -HPAGE_PMD_NR);
 		return;
 	}