platform/chrome: cros_ec_vbc: 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_vbc.c

@@ -40,7 +40,7 @@ static ssize_t vboot_context_read(struct file *filp, struct kobject *kobj,
 	msg->outsize = para_sz;
 	msg->insize = resp_sz;
 
-	err = cros_ec_cmd_xfer(ecdev, msg);
+	err = cros_ec_cmd_xfer_status(ecdev, msg);
 	if (err < 0) {
 		dev_err(dev, "Error sending read request: %d\n", err);
 		kfree(msg);
@@ -83,7 +83,7 @@ static ssize_t vboot_context_write(struct file *filp, struct kobject *kobj,
 	msg->outsize = para_sz;
 	msg->insize = 0;
 
-	err = cros_ec_cmd_xfer(ecdev, msg);
+	err = cros_ec_cmd_xfer_status(ecdev, msg);
 	if (err < 0) {
 		dev_err(dev, "Error sending write request: %d\n", err);
 		kfree(msg);