[S390] driver_data access

Replace the remaining direct accesses to the driver_data pointer
with calls to the dev_get_drvdata() and dev_set_drvdata() functions.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/char/tape_core.c b/drivers/s390/char/tape_core.c
index 595aa04..1d420d9 100644
--- a/drivers/s390/char/tape_core.c
+++ b/drivers/s390/char/tape_core.c
@@ -396,7 +396,7 @@
 {
 	struct tape_device *device;
 
-	device = cdev->dev.driver_data;
+	device = dev_get_drvdata(&cdev->dev);
 	if (!device) {
 		return -ENODEV;
 	}