ACPI: thermal: Clean up acpi_thermal_register_thermal_zone()

Rename the trips variable in acpi_thermal_register_thermal_zone() to
trip_count so its name better reflects the purpose, rearrange white
space in the loop over active trips for clarity and reduce code
duplication related to calling thermal_zone_device_register() by
using an extra local variable to store the passive delay value.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>