OpenBSD: Use osi_obsd_Free() for all releases of OBSD

OpenBSD: Use osi_obsd_Free() for all releases of OBSD

Use osi_obsd_Free() in afs_osi_Free() for all releases of OpenBSD,
not just releases from 4.4 onward. Otherwise, afs_osi_Free() will
use AFS_KFREE, which does not exist, since OBSD/osi_machdep.h is
not included, resulting in unresolved symbols when trying to load
the kernel module.

Change-Id: Ic9632c9df347cc17e122b6302ef14e63fa5b68b4
Reviewed-on: http://gerrit.openafs.org/1910
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>