can: usb_8dev: unregister netdev before free()ing

The usb_8dev hardware has problems on some xhci USB hosts. The driver fails to
read the firmware revision in the probe function. This leads to the following
Oops:

    [ 3356.635912] kernel BUG at net/core/dev.c:5701!

The driver tries to free the netdev, which has already been registered, without
unregistering it.

This patch fixes the problem by unregistering the netdev in the error path.
Reported-by: Michael Olbrich <m.olbrich@pengutronix.de>
Reviewed-by: Bernd Krumboeck <krumboeck@universalnet.at>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/usb_8dev.c

@@ -977,7 +977,7 @@ static int usb_8dev_probe(struct usb_interface *intf,
 	err = usb_8dev_cmd_version(priv, &version);
 	if (err) {
 		netdev_err(netdev, "can't get firmware version\n");
-		goto cleanup_cmd_msg_buffer;
+		goto cleanup_unregister_candev;
 	} else {
 		netdev_info(netdev,
 			 "firmware: %d.%d, hardware: %d.%d\n",
@@ -989,6 +989,9 @@ static int usb_8dev_probe(struct usb_interface *intf,
 
 	return 0;
 
+cleanup_unregister_candev:
+	unregister_netdev(priv->netdev);
+
 cleanup_cmd_msg_buffer:
 	kfree(priv->cmd_msg_buffer);