[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/css.c b/drivers/s390/cio/css.c
index c3df2cd..bc2f8fa 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -787,8 +787,8 @@
 static int
 css_bus_match (struct device *dev, struct device_driver *drv)
 {
-	struct subchannel *sch = container_of (dev, struct subchannel, dev);
-	struct css_driver *driver = container_of (drv, struct css_driver, drv);
+	struct subchannel *sch = to_subchannel(dev);
+	struct css_driver *driver = to_cssdriver(drv);
 
 	if (sch->st == driver->subchannel_type)
 		return 1;
@@ -802,7 +802,7 @@
 	struct subchannel *sch;
 
 	sch = to_subchannel(dev);
-	sch->driver = container_of (dev->driver, struct css_driver, drv);
+	sch->driver = to_cssdriver(dev->driver);
 	return (sch->driver->probe ? sch->driver->probe(sch) : 0);
 }