MAINTAINERS: Add Daniel Lezcano as designated reviewer for thermal

Add Daniel Lezcano as the reviewer for thermal as he would like to
participate in the review process effort for the thermal framework,
especially the SoC part.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>