ACPI: PCI: use positive logic to simplify code

This doesn't change anything functionally; it just changes tests
so we test for success instead of failure.  This makes the code
read more easily and allows us to remove the "!entry" in the while
loop condition.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>