volser: Actually return errors from ListOneVolume

volser: Actually return errors from ListOneVolume

The return code from GetVolInfo was being thrown away, and success
returned to the caller, regardless of the success of this function.
As GetVolInfo's exit codes aren't suitable for sending over the wire,
just return ENODEV if this function returns failure.

Change-Id: Ie4adbbd98f5006a9aa50ed9bf73ea9e4344fabf3
Reviewed-on: http://gerrit.openafs.org/5000
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>