[S390] tape: fix tape remove function

Fix a bug introduced with git commit dff59b64:
 -       if (cdev->dev.driver_data != NULL) {
 +       if (!dev_get_drvdata(&cdev->dev)) {
These two are not equivalent.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/tape_core.c

@@ -665,7 +665,7 @@ tape_generic_remove(struct ccw_device *cdev)
 			tape_cleanup_device(device);
 	}
 
-	if (!dev_get_drvdata(&cdev->dev)) {
+	if (dev_get_drvdata(&cdev->dev)) {
 		sysfs_remove_group(&cdev->dev.kobj, &tape_attr_group);
 		dev_set_drvdata(&cdev->dev, tape_put_device(dev_get_drvdata(&cdev->dev)));
 	}