cros_ec_check_result() is used to check if the EC communication success but
EC responded EC_RES_IN_PROGRESS.  It should return 0 even if EC wasn't
happy about the host command.

Add Kunit tests for cros_ec_check_result().
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20220518091814.2028579-5-tzungbi@kernel.org