sx8: use the internal state machine to check if del_gendisk needs to be called

Remove usage of the block layer internal GENHD_FL_UP by just looking
at the host state.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210809064028.1198327-6-hch@lst.de


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