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: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: NZhang Rui <rui.zhang@intel.com>
Reviewed-by: NZhang Rui <rui.zhang@intel.com>