ACPI / processor: Fix acpi_processor_eval_pdc() return value type

The return value type of acpi_processor_eval_pdc() should be
'acpi_status' but is defined as 'int', so fix it.

Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>