platform/chrome: cros_ec_proto: update Kunit test for get_next_data_v3

platform/chrome: cros_ec_proto: update Kunit test for get_next_data_v3

Since commit 106d67398233 ("platform/chrome: cros_ec_proto: Upgrade
get_next_event to v3"), (struct cros_ec_device *)->event_data becomes
struct ec_response_get_next_event_v3.

Update the Kunit test for fixing the following error:
> Expected mock->msg.insize == sizeof(union ec_response_get_next_data_v1), but
>     mock->msg.insize == 18 (0x12)
>     sizeof(union ec_response_get_next_data_v1) == 16 (0x10)

Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20240611033113.4154548-1-tzungbi@kernel.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>