mm/interval_tree.c: use vma_pages() helper

Use vma_pages function on vma object instead of explicit computation.

  mm/interval_tree.c:21:27-33: WARNING: Consider using vma_pages helper

Generated by: scripts/coccinelle/api/vma_pages.cocci

Link: http://lkml.kernel.org/r/1511364410-13499-1-git-send-email-gomonovych@gmail.comSigned-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/interval_tree.c

@@ -18,7 +18,7 @@ static inline unsigned long vma_start_pgoff(struct vm_area_struct *v)
 
 static inline unsigned long vma_last_pgoff(struct vm_area_struct *v)
 {
-	return v->vm_pgoff + ((v->vm_end - v->vm_start) >> PAGE_SHIFT) - 1;
+	return v->vm_pgoff + vma_pages(v) - 1;
 }
 
 INTERVAL_TREE_DEFINE(struct vm_area_struct, shared.rb,