can: peak_usb: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/peak_usb/pcan_usb.c

@@ -423,6 +423,7 @@ static int pcan_usb_decode_error(struct pcan_usb_msg_context *mc, u8 n,
 			new_state = CAN_STATE_ERROR_WARNING;
 			break;
 		}
+		/* else: fall through */
 
 	case CAN_STATE_ERROR_WARNING:
 		if (n & PCAN_USB_ERROR_BUS_HEAVY) {

drivers/net/can/usb/peak_usb/pcan_usb_core.c

@@ -353,6 +353,7 @@ static netdev_tx_t peak_usb_ndo_start_xmit(struct sk_buff *skb,
 		default:
 			netdev_warn(netdev, "tx urb submitting failed err=%d\n",
 				    err);
+			/* fall through */
 		case -ENOENT:
 			/* cable unplugged */
 			stats->tx_dropped++;

drivers/net/can/usb/peak_usb/pcan_usb_pro.c

@@ -141,8 +141,10 @@ static int pcan_msg_add_rec(struct pcan_usb_pro_msg *pm, u8 id, ...)
 	switch (id) {
 	case PCAN_USBPRO_TXMSG8:
 		i += 4;
+		/* fall through */
 	case PCAN_USBPRO_TXMSG4:
 		i += 4;
+		/* fall through */
 	case PCAN_USBPRO_TXMSG0:
 		*pc++ = va_arg(ap, int);
 		*pc++ = va_arg(ap, int);