volinfo: fix formating of placeholder printfs

needed to placate gcc-llvm on lion

Reviewed-on: http://gerrit.openafs.org/6565
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 60df98806b1aaf6ea4ba8f089faf8e9247b2fba5)

Change-Id: I583cc194ad81b025f925ad56a74c4acd941b7ddf
Reviewed-on: http://gerrit.openafs.org/11269
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>