MAINTAINERS: Add Prashant's maintainership of cros_ec drivers

Prashant maintains the cros_usbpd_notify driver as well as
the cros_ec_type_c driver.

Link: https://lore.kernel.org/r/20210920205402.3818320-1-bleung@chromium.org


Signed-off-by: Benson Leung <bleung@chromium.org>
Acked-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>