mm/page-writeback.c: update stale account_page_redirty() comment

Commit 93f78d8 ("writeback: move backing_dev_info->bdi_stat[] into
bdi_writeback") replaced BDI_DIRTIED with WB_DIRTIED in
account_page_redirty().  Update comment to track that change.

  BDI_DIRTIED => WB_DIRTIED
  BDI_WRITTEN => WB_WRITTEN

Link: http://lkml.kernel.org/r/20180625171526.173483-1-gthelen@google.com
Signed-off-by: Greg Thelen <gthelen@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page-writeback.c

@@ -2490,8 +2490,8 @@ EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 
 /*
  * Call this whenever redirtying a page, to de-account the dirty counters
- * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
- * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
+ * (NR_DIRTIED, WB_DIRTIED, tsk->nr_dirtied), so that they match the written
+ * counters (NR_WRITTEN, WB_WRITTEN) in long term. The mismatches will lead to
  * systematic errors in balanced_dirty_ratelimit and the dirty pages position
  * control.
  */