can: Do not call dev_put if restart timer is running upon close

If the restart timer is running due to BUS-OFF and the device is
disconnected an dev_put will decrease the usage counter to -1 thus
blocking the interface removal, resulting in the following dmesg
lines repeating every 10s:
can: notifier: receive list not found for dev can0
can: notifier: receive list not found for dev can0
can: notifier: receive list not found for dev can0
unregister_netdevice: waiting for can0 to become free. Usage count = -1

Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev.c

@@ -609,8 +609,7 @@ void close_candev(struct net_device *dev)
 {
 	struct can_priv *priv = netdev_priv(dev);
 
-	if (del_timer_sync(&priv->restart_timer))
-		dev_put(dev);
+	del_timer_sync(&priv->restart_timer);
 	can_flush_echo_skb(dev);
 }
 EXPORT_SYMBOL_GPL(close_candev);