platform/chrome: cros_ec_proto: return -EPROTO if empty payload

cros_ec_wait_until_complete() sends EC_CMD_GET_COMMS_STATUS which expects
to receive sizeof(struct ec_response_get_comms_status) from
cros_ec_xfer_command().

Return -EPROTO if cros_ec_xfer_command() returns 0.
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220718050914.2267370-11-tzungbi@kernel.org

drivers/platform/chrome/cros_ec_proto.c

@@ -163,6 +163,11 @@ static int cros_ec_wait_until_complete(struct cros_ec_device *ec_dev, uint32_t *
 		if (msg->result != EC_RES_SUCCESS)
 			return ret;
 
+		if (ret == 0) {
+			ret = -EPROTO;
+			break;
+		}
+
 		if (!(status->flags & EC_COMMS_STATUS_PROCESSING))
 			return ret;
 	}