platform/chrome: cros_ec: Use cros_ec_cmd_xfer_status helper

This patch makes use of cros_ec_cmd_xfer_status() instead of
cros_ec_cmd_xfer(). In this case the change is trivial and the only
reason to do it is because we want to make cros_ec_cmd_xfer() a private
function for the EC protocol and let people only use the
cros_ec_cmd_xfer_status() to return Linux standard error codes.
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: Prashant Malani <pmalani@chromium.org>

drivers/platform/chrome/cros_ec.c

@@ -120,7 +120,7 @@ static int cros_ec_sleep_event(struct cros_ec_device *ec_dev, u8 sleep_event)
 
 	buf.msg.command = EC_CMD_HOST_SLEEP_EVENT;
 
-	ret = cros_ec_cmd_xfer(ec_dev, &buf.msg);
+	ret = cros_ec_cmd_xfer_status(ec_dev, &buf.msg);
 
 	/* For now, report failure to transition to S0ix with a warning. */
 	if (ret >= 0 && ec_dev->host_sleep_v1 &&