volinfo: initialize vnode details

Clear the vnode details object. Fixes the path lookup in volscan.

Reviewed-on: http://gerrit.openafs.org/6722
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit e5e9260c7936ce0b4d51855291421679acccaed4)

Change-Id: If9848191166a774e99e68410d7891564743975e5
Reviewed-on: http://gerrit.openafs.org/11270
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>