MAINTAINERS: update thermal entry by adding file cpu_cooling.h

Add cpu_cooling.h to thermal entry in MAINTAINERS.

Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Acked-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Acked-by: Zhang Rui <rui.zhang@intel.com>