blkcg: fix missing free on error path of blk_iocost_init()

blk_iocost_init() forgot to free its percpu stat on the error path.
Fix it.

Fixes: 7caa4715 ("blkcg: implement blk-iocost")
Reported-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iocost.c

@@ -1876,6 +1876,7 @@ static int blk_iocost_init(struct request_queue *q)
 	ret = blkcg_activate_policy(q, &blkcg_policy_iocost);
 	if (ret) {
 		rq_qos_del(q, rqos);
+		free_percpu(ioc->pcpu_stat);
 		kfree(ioc);
 		return ret;
 	}