can: usb_8dev: fix use-after-free on disconnect

The driver was accessing its driver data after having freed it.

Fixes: 0024d8ad ("can: usb_8dev: Add support for USB2CAN interface from 8 devices")
Cc: stable <stable@vger.kernel.org>     # 3.9
Cc: Bernd Krumboeck <b.krumboeck@gmail.com>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: NJohan Hovold <johan@kernel.org>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/usb_8dev.c

@@ -996,9 +996,8 @@ static void usb_8dev_disconnect(struct usb_interface *intf)
 		netdev_info(priv->netdev, "device disconnected\n");
 
 		unregister_netdev(priv->netdev);
-		free_candev(priv->netdev);
-
 		unlink_all_urbs(priv);
+		free_candev(priv->netdev);
 	}
 
 }