IRIX: set vfs pointer when creating new vcaches

IRIX: set vfs pointer when creating new vcaches

add missing call to set our vfsp on irix.

Reviewed-on: http://gerrit.openafs.org/4561
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 7d72a8c5c4b9df417c9337c01e8a7f26d8f6280b)

Change-Id: If0cccaa47f1110eca347734bfbaedc0456e53b21
Reviewed-on: http://gerrit.openafs.org/4579
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>