ncpfs: 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>

fs/ncpfs/mmap.c

@@ -117,7 +117,7 @@ int ncp_mmap(struct file *file, struct vm_area_struct *vma)
 		return -EINVAL;
 	/* we do not support files bigger than 4GB... We eventually 
 	   supports just 4GB... */
-	if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff 
+	if (vma_pages(vma) + vma->vm_pgoff
 	   > (1U << (32 - PAGE_SHIFT)))
 		return -EFBIG;