MAINTAINERS: Add entry for SAMSUNG THERMAL DRIVER

This patch adds entry for SAMSUNG THERMAL DRIVER in the MAINTAINERS file.
It has been agreed, that pull request are going to be sent to Eduardo
Valentin.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Acked-by: Eduardo Valentin <edubezval@gmail.com>