Modify pch_wpt_add_acpi_psv_trip() to return an int value instead of
using a return pointer for that.

While at it, drop an excessive empty code line.
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>