can: esd_usb: Improve readability on decoding ESD_EV_CAN_ERROR_EXT messages

As suggested by Marc introduce a union plus a struct ev_can_err_ext
for easier decoding of an ESD_EV_CAN_ERROR_EXT event message (which
simply is a rx_msg with some dedicated data).
Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/linux-can/20220621071152.ggyhrr5sbzvwpkpx@pengutronix.de/Signed-off-by: Frank Jungclaus <frank.jungclaus@esd.eu>
Link: https://lore.kernel.org/all/20230216190450.3901254-4-frank.jungclaus@esd.euSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/esd_usb.c

@@ -127,7 +127,15 @@ struct rx_msg {
 	u8 dlc;
 	__le32 ts;
 	__le32 id; /* upper 3 bits contain flags */
-	u8 data[8];
+	union {
+		u8 data[8];
+		struct {
+			u8 status; /* CAN Controller Status */
+			u8 ecc;    /* Error Capture Register */
+			u8 rec;    /* RX Error Counter */
+			u8 tec;    /* TX Error Counter */
+		} ev_can_err_ext;  /* For ESD_EV_CAN_ERROR_EXT */
+	};
 };
 
 struct tx_msg {
@@ -229,10 +237,10 @@ static void esd_usb_rx_event(struct esd_usb_net_priv *priv,
 	u32 id = le32_to_cpu(msg->msg.rx.id) & ESD_IDMASK;
 
 	if (id == ESD_EV_CAN_ERROR_EXT) {
-		u8 state = msg->msg.rx.data[0];
-		u8 ecc = msg->msg.rx.data[1];
-		u8 rxerr = msg->msg.rx.data[2];
-		u8 txerr = msg->msg.rx.data[3];
+		u8 state = msg->msg.rx.ev_can_err_ext.status;
+		u8 ecc = msg->msg.rx.ev_can_err_ext.ecc;
+		u8 rxerr = msg->msg.rx.ev_can_err_ext.rec;
+		u8 txerr = msg->msg.rx.ev_can_err_ext.tec;
 
 		netdev_dbg(priv->netdev,
 			   "CAN_ERR_EV_EXT: dlc=%#02x state=%02x ecc=%02x rec=%02x tec=%02x\n",