Windows: cm_GetSCache do not release unheld lock

Windows: cm_GetSCache do not release unheld lock

if cm_GetNewSCache() fails, an attempt would be made to
release cm_scacheLock which is not held.  However, it should
be noted that cm_GetNewSCache() cannot fail without itself
triggering a panic.

Reviewed-on: http://gerrit.openafs.org/6103
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit d42db13152fb8fa374db6531020da6effca51ab4)

Change-Id: Ibb3aff0a256c6846ac8b9336a50ea021f8a1e2f6
Reviewed-on: http://gerrit.openafs.org/6809
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>