fs/writeback: correct comment of __wakeup_flusher_threads_bdi

Commit e8e8a0c ("writeback: move nr_pages == 0 logic to one
location") removed parameter nr_pages of __wakeup_flusher_threads_bdi
and we try to writeback all dirty pages in __wakeup_flusher_threads_bdi
now. Just correct stale comment.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Link: https://lore.kernel.org/r/20240228091958.288260-6-shikemeng@huaweicloud.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Kemeng Shi

fs/fs-writeback.c

@@ -2332,8 +2332,7 @@ void wb_workfn(struct work_struct *work)
 }
 
 /*
- * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
- * write back the whole world.
+ * Start writeback of all dirty pages on this bdi.
  */
 static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
 					 enum wb_reason reason)