vlserver: unsigned values are always >0

vlserver: unsigned values are always >0

Maxvolidbump is defined as an unisgned int, and thus can never be less
than 0. Remove the pointless check, as it just makes clang sad.

Change-Id: I78a2c8f6fcaee17196e37183256e6935cdca183b
Reviewed-on: http://gerrit.openafs.org/7084
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>