thermal: Update information in MAINTAINERS

Because Rui is now going to focus on work that is not related to the
maintenance of the thermal subsystem in the kernel, Rafael will start
to help Daniel with handling the development process as a new member
of the thermal maintainers team.  Rui will continue to review patches
in that area.

The thermal development process flow will change so that the material
from the thermal git tree will be merged into the thermal branch of
the linux-pm.git tree before going into the mainline.

Update the information in MAINTAINERS accordingly.

Signed-off-by: Rafael J. Wysocki <rafael@kernel.org>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>