thermal: disable polling if passive_delay and polling_delay are both unset

Otherwise polling will continue for the thermal zone even when
it is no longer needed, for example because forced passive cooling
was disabled.

Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Matthew Garrett <mjg@redhat.com>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>