ACPICA: _CST repair: Handle null package entries

Sort package only after null/bad elements have been removed.

Fixes a problem where the _CST sort was performed too early.  This
change sorts the package only after null/bad elements have been
removed.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>