mfd: qnap-mcu: Use EPROTO in stead of EIO on checksum errors

EPROTO stands for protocol error and a lot of driver already use it
to designate errors in the sent or received data from a peripheral.

So use it in the qnap-mcu as well for checksum errors.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20251113165218.449616-3-heiko@sntech.de
Signed-off-by: Lee Jones <lee@kernel.org>

Author: mmind

drivers/mfd/qnap-mcu.c

@@ -178,7 +178,7 @@ int qnap_mcu_exec(struct qnap_mcu *mcu,
 	crc = qnap_mcu_csum(rx, reply->received - QNAP_MCU_CHECKSUM_SIZE);
 	if (crc != rx[reply->received - QNAP_MCU_CHECKSUM_SIZE]) {
 		dev_err(&mcu->serdev->dev, "Invalid Checksum received\n");
-		return -EIO;
+		return -EPROTO;
 	}
 
 	memcpy(reply_data, rx, reply_data_size);