can: slcan: do not report txerr and rxerr during bus-off

During bus off, the error count is greater than 255 and can not fit in
a u8.

alloc_can_err_skb() already sets cf to NULL if the allocation fails [1],
so the redundant cf = NULL assignment gets removed.

[1] https://elixir.bootlin.com/linux/latest/source/drivers/net/can/dev/skb.c#L187

Fixes: 0a9cdcf0 ("can: slcan: extend the protocol with CAN state info")
Link: https://lore.kernel.org/all/20220719143550.3681-5-mailhol.vincent@wanadoo.fr
CC: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/slcan/slcan-core.c

@@ -306,19 +306,17 @@ static void slc_bump_state(struct slcan *sl)
 		return;
 
 	skb = alloc_can_err_skb(dev, &cf);
-	if (skb) {
-		cf->data[6] = txerr;
-		cf->data[7] = rxerr;
-	} else {
-		cf = NULL;
-	}
 
 	tx_state = txerr >= rxerr ? state : 0;
 	rx_state = txerr <= rxerr ? state : 0;
 	can_change_state(dev, cf, tx_state, rx_state);
 
-	if (state == CAN_STATE_BUS_OFF)
+	if (state == CAN_STATE_BUS_OFF) {
 		can_bus_off(dev);
+	} else if (skb) {
+		cf->data[6] = txerr;
+		cf->data[7] = rxerr;
+	}
 
 	if (skb)
 		netif_rx(skb);