[S390] cio: Use helpers instead of container_of().

- Introduce to_cssdriver.
- Use to_xxx instead of container_of where possible.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/ccwgroup.c b/drivers/s390/cio/ccwgroup.c
index 5baa517..b3e2c16 100644
--- a/drivers/s390/cio/ccwgroup.c
+++ b/drivers/s390/cio/ccwgroup.c
@@ -35,8 +35,8 @@
 	struct ccwgroup_device *gdev;
 	struct ccwgroup_driver *gdrv;
 
-	gdev = container_of(dev, struct ccwgroup_device, dev);
-	gdrv = container_of(drv, struct ccwgroup_driver, driver);
+	gdev = to_ccwgroupdev(dev);
+	gdrv = to_ccwgroupdrv(drv);
 
 	if (gdev->creator_id == gdrv->driver_id)
 		return 1;