mfd: cros_ec: Add cros_ec_cmd_xfer_status() helper

mfd: cros_ec: Add cros_ec_cmd_xfer_status() helper

commit 9798ac6d32c1a32d6d92d853ff507d2d39c4300c upstream.

So that callers of cros_ec_cmd_xfer() don't have to repeat boilerplate
code when checking for errors from the EC side.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>