util: fix dirpath use of clntEtcDir on Windows

When commit 9b0a7f5d13115fe5760db16587fe81dd35a5a0ef added the variable
'clntEtcDir' it failed to assign it a value on Windows.

Change-Id: I02cfb994a28e3e1032741d1b2710acb5d40d9bfd
Reviewed-on: http://gerrit.openafs.org/9635
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>