platform/chrome: cros_ec_proto: assign buffer size from protocol info

`din_size` is calculated from `ec_dev->max_response`.
`ec_dev->max_response` is further calculated from the protocol info.

To make it clear, assign `din_size` and `dout_size` from protocol info
directly.

Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220609084957.3684698-5-tzungbi@kernel.org