blk-mq: set default timeout as 30 seconds

It is reasonable to set default timeout of request as 30 seconds instead of
30000 ticks, which may be 300 seconds if HZ is 100, for example, some arm64
based systems may choose 100 HZ.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Fixes: c76cbbcf ("blk-mq: put blk_queue_rq_timeout together in blk_mq_init_queue()"
Signed-off-by: NJens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -1998,7 +1998,7 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 		goto err_hctxs;
 
 	setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
-	blk_queue_rq_timeout(q, set->timeout ? set->timeout : 30000);
+	blk_queue_rq_timeout(q, set->timeout ? set->timeout : 30 * HZ);
 
 	q->nr_queues = nr_cpu_ids;
 	q->nr_hw_queues = set->nr_hw_queues;