thermal: testing: Use DEFINE_FREE() and __free() to simplify code

Use DEFINE_FREE() to define a __free function for dropping thermal
zone template reference counters and use it along with __free() to
simplify code in some places.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/4628747.LvFx2qVVIh@rjwysocki.net


[ rjw: Add variable initialization to address compiler warning ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>