uio: use vma_pages() to replace (vm_end - vm_start) >> PAGE_SHIFT

(*->vm_end - *->vm_start) >> PAGE_SHIFT operation is implemented
as a inline funcion vma_pages() in linux/mm.h, so using it.
Signed-off-by: Libin <huawei.libin@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/uio/uio.c

@@ -677,7 +677,7 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 	if (mi < 0)
 		return -EINVAL;
 
-	requested_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	requested_pages = vma_pages(vma);
 	actual_pages = ((idev->info->mem[mi].addr & ~PAGE_MASK)
 			+ idev->info->mem[mi].size + PAGE_SIZE -1) >> PAGE_SHIFT;
 	if (requested_pages > actual_pages)