block: hold a request_queue reference for the lifetime of struct gendisk

Acquire the queue ref dropped in disk_release in __blk_alloc_disk so any
allocate gendisk always has a queue reference.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210816131910.615153-9-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>