s390: drivers: convert to use DRIVER_ATTR_RO/WO

We are trying to get rid of DRIVER_ATTR(), and the s390 drivers'
attributes can be trivially changed to use DRIVER_ATTR_RO() and
DRIVER_ATTR_WO().

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Cc: Ursula Braun <ubraun@linux.vnet.ibm.com>
Cc: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: <linux-s390@vger.kernel.org>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>