X25: Fix oops and refcnt problems from x25_dev_get

Calls to x25_dev_get check for dev = NULL which was not set.
It allowed x25 to set routes and ioctls on down interfaces.
This caused oopses and refcnt problems on device_unregister.
Signed-off-by: Andrew Hendry <andrew.hendry@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/x25/x25_route.c

@@ -136,8 +136,10 @@ struct net_device *x25_dev_get(char *devname)
 #if defined(CONFIG_LLC) || defined(CONFIG_LLC_MODULE)
 					&& dev->type != ARPHRD_ETHER
 #endif
-					)))
+					))){
 		dev_put(dev);
+		dev = NULL;
+	}
 
 	return dev;
 }