ACPI: Fix possible null ptr dereference

Code in `pci_link.c' is calling the internal routine `acpi_ut_evaluate_object'
which is dangerous given that it is passing a NULL pointer when it should
be passing a pointer to a real object.  The patch corrects the issue by
having the code call the external routine `acpi_evaluate_object', which
correctly handles a NULL pointer.

Signed-off-by: Don Dugger <donald.d.dugger@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>