block: release rq qos structures for queue without disk

In the Linux kernel, the following vulnerability has been resolved:

block: release rq qos structures for queue without disk

blkcg_init_queue() may add rq qos structures to request queue, previously

blk_cleanup_queue() calls rq_qos_exit() to release them, but commit

8e141f9eb803 ("block: drain file system I/O on del_gendisk")

moves rq_qos_exit() into del_gendisk(), so memory leak is caused

because queues may not have disk, such as un-present scsi luns, nvme

admin queue, ...

Fixes the issue by adding rq_qos_exit() to blk_cleanup_queue() back.

BTW, v5.18 won't need this patch any more since we move

blkcg_init_queue()/blkcg_exit_queue() into disk allocation/release

handler, and patches have been in for-5.18/block.