MAINTAINERS: add entry for ADM1177 driver

Add Beniamin Bia and Michael Hennerich as a maintainer for ADM1177 ADC.

Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Link: https://lore.kernel.org/r/20200114112159.25998-3-beniamin.bia@analog.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>