ACPI: thermal: Move get_active_temp()

Put the get_active_temp() function next to the analogous
get_passive_temp() one to allow subsequent changes to be easier to
follow.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>