userfaultfd: use helper function range_in_vma()

We can use range_in_vma() to check if dst_start, dst_start + len are
within the dst_vma range.  Minor readability improvement.

Link: https://lkml.kernel.org/r/20230417003919.930515-1-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/userfaultfd.c

@@ -31,11 +31,7 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
 	struct vm_area_struct *dst_vma;
 
 	dst_vma = find_vma(dst_mm, dst_start);
-	if (!dst_vma)
-		return NULL;
-
-	if (dst_start < dst_vma->vm_start ||
-	    dst_start + len > dst_vma->vm_end)
+	if (!range_in_vma(dst_vma, dst_start, dst_start + len))
 		return NULL;
 
 	/*