Windows: close leak in AFSPrimaryVolumeWorkerThread

Windows: close leak in AFSPrimaryVolumeWorkerThread

Prevent a leak of the non-paged pool and a Resource by freeing all
allocations within the Specific.Directory.PIOCtlDirectoryCB object.

Use AFSExFreePool() instead of ExFreePool() because the objects
are allocated from the AFSRedir.sys driver allocator.

FIXES 130280

Change-Id: I3b1c8fa838cfdf434bf7c08bb8935999cf328357
Reviewed-on: http://gerrit.openafs.org/5730
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>