afs: Move SetupVolume tv initialization after loop

The fields in tv are not used by the loop looking for the given volume
on disk. If we wait until after that loop to initialize the fields in
tv, it is easier to handle errors encountered in the loop.

This should incur no functional change.

Change-Id: Ib678542bfebaa89ecfa4aad39230fc502ec83edb
Reviewed-on: http://gerrit.openafs.org/9093
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>