MAINTAINERS: Add linux-omap to list of reviewers for TI Thermal

Add linux-omap mailing list to the TI THERMAL list for wider review.

Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>