ACPI: thermal: drop an always true check

commit e5b5d254 upstream.

Address of a field inside a struct can't possibly be null; gcc-12 warns
about this.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>