can: gs_usb: fix return value of the "set_bittiming" callback

The "set_bittiming" callback treats a positive return value as error!
For that reason "can_changelink()" will quit silently after setting
the bittiming values without processing ctrlmode, restart-ms, etc.
Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -449,7 +449,7 @@ static int gs_usb_set_bittiming(struct net_device *netdev)
 		dev_err(netdev->dev.parent, "Couldn't set bittimings (err=%d)",
 			rc);
 
-	return rc;
+	return (rc > 0) ? 0 : rc;
 }
 
 static void gs_usb_xmit_callback(struct urb *urb)