blk-wbt: pass a gendisk to wbt_{enable,disable}_default

Pass a gendisk to wbt_enable_default and wbt_disable_default to
prepare for 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/20230203150400.3199230-9-hch@lst.de


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