volser: fix spurious strcat of volume extension.

Fix malformed merge error left over from
commit 4f9ec8396d1c7f12f8fa264cea7c255ce62b7b8d
where we converted strcat to strlcat.

Reviewed-on: http://gerrit.openafs.org/10963
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit e6110959e802bd9ae60e3724ba41078e7b335bab)

Change-Id: I3ac39245f9151f319ab5d5bb6b6d17dd13446ac1
Reviewed-on: http://gerrit.openafs.org/11039
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>