mmc: block: let device_add_disk create disk attributes

Pass the attribute group for the attributes on the gendisk to
device_add_disk so that they are created atomically with the
disk creation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210809064028.1198327-2-hch@lst.de


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