OpenBSD: Replace "vnodeop_desc" with "vops" in kernel module.

In OpenBSD 4.9, the vnode operations vector in the "vnode" struct
was changed from using a "vnodeop_desc" struct to a new "vops"
struct. This patch makes the appropriate changes to the OpenBSD
kernel module support to accommodate the change.

Change-Id: Ib47259e1213e29658a691ce3a53d7ac88e8d746b
Reviewed-on: http://gerrit.openafs.org/8928
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>