mm: use vma_pages() for vma objects

vma_pages() is more readable and also better at avoiding error codes, so
use vma_pages() instead of direct operations on vma

Link: https://lkml.kernel.org/r/tencent_151850CF327EB055BBC83298A929BD06CD0A@qq.com
Signed-off-by: Chen Haonan <chen.haonan2@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/internal.h

@@ -616,7 +616,7 @@ folio_within_range(struct folio *folio, struct vm_area_struct *vma,
 		unsigned long start, unsigned long end)
 {
 	pgoff_t pgoff, addr;
-	unsigned long vma_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	unsigned long vma_pglen = vma_pages(vma);
 
 	VM_WARN_ON_FOLIO(folio_test_ksm(folio), folio);
 	if (start > end)