volser: fix spurious strcat of volume extension.

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

Change-Id: Ibae3e09c8a659f4b084256b18ee5774f11fe9f8f
Reviewed-on: http://gerrit.openafs.org/10963
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>