mm/rmap: fix comment in anon_vma_clone()

Commit 2555283e ("mm/rmap: Fix anon_vma->degree ambiguity leading to
double-reuse") use num_children and num_active_vmas to replace the origin
degree to fix anon_vma UAF problem.  Update the comment in anon_vma_clone
to fit this change.

Link: https://lkml.kernel.org/r/20221014013931.1565969-1-mawupeng1@huawei.comSigned-off-by: Ma Wupeng <mawupeng1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap.c

@@ -315,8 +315,8 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 
  enomem_failure:
 	/*
-	 * dst->anon_vma is dropped here otherwise its degree can be incorrectly
-	 * decremented in unlink_anon_vmas().
+	 * dst->anon_vma is dropped here otherwise its num_active_vmas can
+	 * be incorrectly decremented in unlink_anon_vmas().
 	 * We can safely do this because callers of anon_vma_clone() don't care
 	 * about dst->anon_vma if anon_vma_clone() failed.
 	 */