blk-cgroup: pass a gendisk to blkg_lookup

Pass a gendisk to blkg_lookup and use that to find the match as part
of phasing out usage of the request_queue in the blk-cgroup code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230203150400.3199230-19-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>