Windows: AFSDeleteObjectInfo InterlockedCompareExchangePointer

Correct the third parameter passed to InterlockedCompareExchangePointer
in AFSDeleteObjectInfo() which prevented *ppObjectInfo from being set
to NULL.

Change-Id: I4edc1d69114c02ffff8181b176a5f0bac82f6802
Reviewed-on: http://gerrit.openafs.org/9689
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>