blk-iocost: pass a gendisk to blk_iocost_init

Pass the gendisk to blk_iocost_init as part of moving the blk-cgroup
infrastructure to be gendisk based.

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/20220921180501.1539876-11-hch@lst.de


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