mm: hugetlb_vmemmap: use PTRS_PER_PTE instead of PMD_SIZE / PAGE_SIZE

There is already a macro PTRS_PER_PTE to represent the number of page
table entries, just use it.

Link: https://lkml.kernel.org/r/20220628092235.91270-9-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Will Deacon <will@kernel.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hugetlb_vmemmap.c

@@ -48,7 +48,7 @@ static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
 
 	pmd_populate_kernel(&init_mm, &__pmd, pgtable);
 
-	for (i = 0; i < PMD_SIZE / PAGE_SIZE; i++, addr += PAGE_SIZE) {
+	for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
 		pte_t entry, *pte;
 		pgprot_t pgprot = PAGE_KERNEL;