swim3: use bdev_check_media_changed

Switch to use bdev_check_media_changed instead of check_disk_change and
call floppy_revalidate manually.  Given that floppy_revalidate only
deals with media change events, the extra call into ->revalidate_disk
from bdev_disk_changed is not required either, so stop wiring up the
method.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>