Windows: cm_UpdateVolumeLocation misplaced lock

Windows: cm_UpdateVolumeLocation misplaced lock

The volume->mx was obtained in the wrong place which resulted
in the potential of a panic caused by obtaining the mutex when
it was already held.

Reviewed-on: http://gerrit.openafs.org/7654
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 4707174938b92df189697a2b7e463438c37c1ed0)

Change-Id: I151547ec9f90f17ae28397c77337b92ea7919754
Reviewed-on: http://gerrit.openafs.org/8635
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>