blk_release_queue — release a struct request_queue when it is no longer needed
|struct kobject * kobj|
blk_release_queue is the pair to
blk_queue_make_request. It should be called when a request queue is
being released; typically when a block device is being de-registered.
Currently, its primary task it to free all the struct request
structures that were allocated to the queue and the queue itself.
The low level driver must have finished any outstanding requests first