ACPI: elide a non-zero test on a result that is never 0

thermal_cooling_device_register used to return NULL if THERMAL is "n".
As the ACPI fan, processor and video drivers SELECT the generic
thermal in PATCH 01, this is not a problem any more.

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>