s390: remove driver_data direct access of struct device

In the near future, the driver core is going to not allow direct access
to the driver_data pointer in struct device.  Instead, the functions
dev_get_drvdata() and dev_set_drvdata() should be used.  These functions
have been around since the beginning, so are backwards compatible with
all older kernel versions.

Thanks to Sebastian Ott <sebott@linux.vnet.ibm.com> for fixing a few
typos in my original version of this patch.

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: linux390@de.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>