s390/cio: remove ccw_device_add() wrapper

Set the bus type when initializing the cdev structure. The device core
won't act on it until we call device_add().

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>