platform/chrome : Add myself as Maintainer

I'll be taking over maintainership of platform/chrome from Olof,
so let's add me to the list of maintainers.

Signed-off-by: Benson Leung <bleung@chromium.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Olof Johansson <olof@lixom.net>