thermal: intel: pch_thermal: Use thermal driver device to write a trace

The pch_critical() callback accesses the thermal zone device structure
internals, it dereferences the thermal zone struct device and the 'type'.

Use the available accessors instead of accessing the structure directly.

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