can: dev: can_restart(): remove unused code

Value assigned to variable err is overwritten at line
562: err = priv->do_set_mode(dev, CAN_MODE_START); before
it can be used.

Also, notice that this code has been there since 2014.

Addresses-Coverity-ID: 1227031
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev.c

@@ -553,10 +553,9 @@ static void can_restart(struct net_device *dev)
 
 	/* send restart message upstream */
 	skb = alloc_can_err_skb(dev, &cf);
-	if (!skb) {
-		err = -ENOMEM;
+	if (!skb)
 		goto restart;
-	}
+
 	cf->can_id |= CAN_ERR_RESTARTED;
 
 	netif_rx(skb);