block/bfq: Enable I/O statistics

BFQ uses io_start_time_ns. That member variable is only set if I/O
statistics are enabled. Hence this patch that enables I/O statistics
at the time BFQ is associated with a request queue.

Compile-tested only.
Reported-by: NCixi Geng <cixi.geng1@unisoc.com>
Cc: Cixi Geng <cixi.geng1@unisoc.com>
Cc: Yu Kuai <yukuai3@huawei.com>
Cc: Paolo Valente <paolo.valente@unimore.it>
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -7046,6 +7046,7 @@ static void bfq_exit_queue(struct elevator_queue *e)
 	spin_unlock_irq(&bfqd->lock);
 #endif
 
+	blk_stat_disable_accounting(bfqd->queue);
 	wbt_enable_default(bfqd->queue);
 
 	kfree(bfqd);
@@ -7192,6 +7193,8 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
 
 	wbt_disable_default(q);
+	blk_stat_enable_accounting(q);
+
 	return 0;
 
 out_free: