MAINTAINERS: add maintainers for Synopsis Designware I2C drivers

Those guys already have been helpful in the past and are actively
working on this driver, unlike me.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>