blk_cleanup_queue — release a &request_queue_t when it is no longer needed
void blk_cleanup_queue (request_queue_t * q);
blk_cleanup_queue is the pair to blk_init_queue or
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.