gigaset: fix possible oops in error handling

Use pr_warning() / pr_err() instead of dev_warn() / dev_err() in two
places where the dev pointer isn't guaranteed to be valid.

Impact: error handling bugfix
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/interface.c

@@ -599,8 +599,7 @@ void gigaset_if_init(struct cardstate *cs)
 	if (!IS_ERR(cs->tty_dev))
 		dev_set_drvdata(cs->tty_dev, cs);
 	else {
-		dev_warn(cs->dev,
-			 "could not register device to the tty subsystem\n");
+		pr_warning("could not register device to the tty subsystem\n");
 		cs->tty_dev = NULL;
 	}
 	mutex_unlock(&cs->mutex);