staging: Convert to bdops->check_events()

staging: Convert to bdops->check_events()

Convert two staging drivers - blkvsc_drv and cyasblkdev_block - from
->media_changed() to ->check_events().  The former always indicated
media changed while the latter always indicated media not changed.
Not sure what the drivers are trying to achieve but keep the original
behavior.

Signed-off-by: Tejun Heo <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Kay Sievers <[email protected]>