[S390] dasd: fix possible NULL pointer errors

Fix possible NULL pointer in DASD messages and correct discipline
checking.

Signed-off-by: Stefan Haberland <stefan.haberland@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index fdb2e7c..5905936 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -1004,8 +1004,8 @@
 	if (device == NULL ||
 	    device != dasd_device_from_cdev_locked(cdev) ||
 	    strncmp(device->discipline->ebcname, (char *) &cqr->magic, 4)) {
-		DBF_DEV_EVENT(DBF_DEBUG, device, "invalid device in request: "
-			      "bus_id %s", dev_name(&cdev->dev));
+		DBF_EVENT_DEVID(DBF_DEBUG, cdev, "%s",
+				"invalid device in request");
 		return;
 	}
 
@@ -1078,8 +1078,8 @@
 	device = (struct dasd_device *) cqr->startdev;
 	if (!device ||
 	    strncmp(device->discipline->ebcname, (char *) &cqr->magic, 4)) {
-		DBF_DEV_EVENT(DBF_DEBUG, device, "invalid device in request: "
-			      "bus_id %s", dev_name(&cdev->dev));
+		DBF_EVENT_DEVID(DBF_DEBUG, cdev, "%s",
+				"invalid device in request");
 		return;
 	}