Windows: Use AFS_OBJECT_REFERENCE_MAX in struct

Use AFS_OBJECT_REFERENCE_MAX to size the array in the struct.
This should have been a part of patchset
e267774f1a4f9cc5bfc32c545df36a4bf7947607.

Change-Id: I9323387a27a5bc2e708f8a8424cb38b491d542d7
Reviewed-on: http://gerrit.openafs.org/9066
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>