freebsd: properly track vcache references

freebsd: properly track vcache references

previously both root and reclaim could end up leaking refs. fix it.

Reviewed-on: http://gerrit.openafs.org/3424
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 6eb1088aad9163ab8d4a4dda513444290c55daa6)
Change-Id: I0c5c8554caf777e8c97529a7d640a79211a0300c
Reviewed-on: http://gerrit.openafs.org/3450