don't release Volume lightweight ref too early

don't release Volume lightweight ref too early

FSYNC_com_VolOff was releasing its lightweight ref before the error handling
code for VGetVolumeByVp_r was executed; this code needs to dereference the
Volume pointer for some of its logic.  This was unsafe since
VCancelReservation_r() could have resulted in the Volume object being freed.
Move VCancelReservation_r() below the error handling block.  NB: the error
handling block now relies upon the goto done/deny to cancel its lightweight
ref.

Change-Id: Ic920e45d55f7d1773585a5c0b004c722355b5725
Reviewed-on: http://gerrit.openafs.org/2968
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>