thermal: Add myself as thermal reviewer in MAINTAINERS

Become designated reviewer and help thermal subsystem in development
process.
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -21363,6 +21363,7 @@ THERMAL
 M:	Rafael J. Wysocki <rafael@kernel.org>
 M:	Daniel Lezcano <daniel.lezcano@linaro.org>
 R:	Zhang Rui <rui.zhang@intel.com>
+R:	Lukasz Luba <lukasz.luba@arm.com>
 L:	linux-pm@vger.kernel.org
 S:	Supported
 Q:	https://patchwork.kernel.org/project/linux-pm/list/