i2c: cros-ec-tunnel: Fix usage of cros_ec_cmd_xfer()

i2c: cros-ec-tunnel: Fix usage of cros_ec_cmd_xfer()

commit 4d01d88019261d05ec3bff5f1a6013393faa3b9e upstream.

cros_ec_cmd_xfer returns success status if the command transport
completes successfully, but the execution result is incorrectly ignored.
In many cases, the execution result is assumed to be successful, leading
to ignored errors and operating on uninitialized data.

We've recently introduced the cros_ec_cmd_xfer_status() helper to avoid these
problems. Let's use it.

[Regarding the 'Fixes' tag; there is significant refactoring since the driver's
introduction, but the underlying logical error exists throughout I believe]

Fixes: 9d230c9e4f4e ("i2c: ChromeOS EC tunnel driver")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>