platform/chrome: cros_ec_chardev: 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_chardev.c

@@ -301,7 +301,7 @@ static long cros_ec_chardev_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
 	}
 
 	s_cmd->command += ec->cmd_offset;
-	ret = cros_ec_cmd_xfer(ec->ec_dev, s_cmd);
+	ret = cros_ec_cmd_xfer_status(ec->ec_dev, s_cmd);
 	/* Only copy data to userland if data was received. */
 	if (ret < 0)
 		goto exit;