Properly handle NULL entries in _PRT return packages.

This change enables proper handling of NULL package entries in a _PRT
return value, during construction of the PCI routing table.
Lv Zheng.
Restore code that repairs NULL package elements in return values.

The original code was lost accidently, it was not generated along with the
following commit of mechanism improvements and thus not get merged:

  Commit: 6cb3c06d1ba242c10e01ee8be73f6dc6d8c33800
  Subject: [PATCH] Add mechanism for early object repairs on a per-name basis.

  Adds the framework to allow object repairs very early in the
  return object analysis. Enables repairs like string->unicode,
  etc.

This patch restores the implementation of the NULL element repair code for
ACPI_RTYPE_NONE.  In the original design, ACPI_RTYPE_NONE is defined to
collect simple NULL object repairs.
Lv Zheng.