platform/chrome: cros_ec_proto: Update size arg types

cros_ec_cmd() takes 2 size arguments. Update them to be of the more
appropriate type size_t.

Suggested-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220606201825.763788-4-pmalani@chromium.org