ACPI: PCI: Rework acpi_get_pci_dev()

The PCI device returned by acpi_get_pci_dev() needs to be registered,
so if it corresponds to an ACPI device object, the struct acpi_device
representing that object must be registered too and, moreover, it
should be the ACPI companion of the given PCI device.  Thus it should
be sufficient to look for it in the ACPI device object's list of
physical nodes associated with it.

Modify the code accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>