thermal: testing: Initialize some variables annoteded with _free()

Variables annotated with __free() need to be initialized if the function
can return before they get updated for the first time or the attempt to
free the memory pointed to by them upon function return may crash the
kernel.

Fix this issue in some places in the thermal testing code.

Fixes: f6a034f2 ("thermal: Introduce a debugfs-based testing facility")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/12576267.O9o76ZdvQC@rjwysocki.net