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.

Change-Id: I316e33712440c2bd816294ad788ad125ab7b4a73
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>