platform/chrome: kunit: initialize lock for fake ec_dev

cros_ec_cmd_xfer() uses ec_dev->lock.  Initialize it.

Otherwise, dmesg shows the following:
> DEBUG_LOCKS_WARN_ON(lock->magic != lock)
> ...
> Call Trace:
>  ? __mutex_lock
>  ? __warn
>  ? __mutex_lock
>  ...
>  ? cros_ec_cmd_xfer

Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20231003080504.4011337-1-tzungbi@kernel.org


Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>