volinfo: PrintFileNames is namei-only

PrintFileNames only exists on namei, so make sure it's inside a namei
ifdef.

Reviewed-on: http://gerrit.openafs.org/4830
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit fc087f187759398a2646480eca25c1195ed23d22)

Change-Id: Id9cfacd35248389cb513a5470dd75ed5a2a30fb9
Reviewed-on: http://gerrit.openafs.org/11259
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>