ISDN: Missed conversion in drivers/isdn/i4l/isdn_net_lib.c

When changing .exclusive from a number to a pointer, the
validity check should have changed from >=0 to != NULL everywhere.

drivers/isdn/i4l/isdn_net_lib.c

@@ -490,7 +490,7 @@ isdn_net_dev_delete(isdn_net_dev *idev)
 	isdn_net_set_encap(mlp, -1);
 	isdn_net_rmallphone(idev);
 
-	if (idev->exclusive >= 0)
+	if (idev->exclusive)
 		isdn_slot_free(idev->exclusive);
 
 	list_del(&idev->slaves);