blk-mq: update comment for blk_mq_hctx_has_pending()

For now, blk_mq_hctx_has_pending() checks any of ctx, hctx->dispatch
or io scheduler have pending work. So, update the comment accordingly.
Signed-off-by: NYufen Yu <yuyufen@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -59,7 +59,8 @@ static int blk_mq_poll_stats_bkt(const struct request *rq)
 }
 
 /*
- * Check if any of the ctx's have pending work in this hardware queue
+ * Check if any of the ctx, dispatch list or elevator
+ * have pending work in this hardware queue.
  */
 static bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx)
 {