ACPI thermal driver only re-evaluate VALID trip points.

For the broken BIOS show in
http://bugzilla.kernel.org/show_bug.cgi?id=8544
the active[0] is set to invalid at boot time
and it will not be re-evaluated again.
We can still get a single warning message at boot time.

http://marc.info/?l=linux-kernel&m=120496222629983&w=2

http://bugzilla.kernel.org/show_bug.cgi?id=12203

Signed-off-by: Zhang Rui<rui.zhang@intel.com>
Tested-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Len Brown <len.brown@intel.com>