block: cleanup comment for blk_flush_complete_seq

Remove the comment about return value, since it is not valid after
commit 404b8f5a03d84 ("block: cleanup kick/queued handling").

Signed-off-by: Guoqing Jiang <[e-mail]>
Reviewed-by: Nikolay Borisov <[e-mail]>
Reviewed-by: Bart Van Assche <[e-mail]>
Reviewed-by: Chaitanya Kulkarni <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

block/blk-flush.c

···
  *
  * CONTEXT:
  * spin_lock_irq(fq->mq_flush_lock)
- *
- * RETURNS:
- * %true if requests were added to the dispatch queue, %false otherwise.
  */
 static void blk_flush_complete_seq(struct request *rq,
 				   struct blk_flush_queue *fq,