thermal: intel: intel_pch: Eliminate redundant return pointers

Both pch_wpt_init() and pch_wpt_get_temp() can return the proper
result via their return values, so they do not need to use return
pointers.

Modify them accordingly.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>