afs/VNOPS: reduce stack usage

AFSFetchStatus is rather large and is in the stack twice.  Allocating with
osi_AllocSmallSpace will save about 160 bytes of stack.

Reviewed-on: http://gerrit.openafs.org/10964
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit 972585c24b5c193a982570ff9264a1971760f48f)

Change-Id: I5ee4441cd1c09646051e148a67147a2663768d44
Reviewed-on: http://gerrit.openafs.org/11162
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>