blk-integrity: convert to struct device_attribute

An upcoming patch will register the integrity attributes directly with
the struct device kobject.
For this the attributes have to be implemented in terms of
struct device_attribute.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20230309-kobj_release-gendisk_integrity-v3-2-ceccb4493c46@weissschuh.net
Signed-off-by: Jens Axboe <axboe@kernel.dk>