[S390] BUG to BUG_ON changes

Signed-off-by: Stoyan Gaydarov <stoyboyker@gmail.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/char/tape_std.c b/drivers/s390/char/tape_std.c
index 44dd0f8..1a9420b 100644
--- a/drivers/s390/char/tape_std.c
+++ b/drivers/s390/char/tape_std.c
@@ -37,8 +37,8 @@
 	int rc;
 
 	request = (struct tape_request *) data;
-	if ((device = request->device) == NULL)
-		BUG();
+	device = request->device;
+	BUG_ON(!device);
 
 	DBF_EVENT(3, "%08x: Assignment timeout. Device busy.\n",
 			device->cdev_id);