emulators/virtualbox-ose: fix builds on CURRENT

SAVENAME was retired by D36542 https://reviews.freebsd.org/D36542

Bug 267079 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=267079
involves failures to build four ports, for VirtualBox guest additions,
on FreeBSD-CURRENT:

emulators/virtualbox-ose-additions
emulators/virtualbox-ose-additions-legacy
emulators/virtualbox-ose-additions-nox11
emulators/virtualbox-ose-additions-nox11-legacy

Fix bug 267079 for CURRENT 1400068 and greater by hiding the use of
SAVENAME in patch-src_VBox_Additions_freebsd_vboxvfs_vboxvfs__vnops.c
for:

emulators/virtualbox-ose
emulators/virtualbox-ose-legacy

PR: : 267079
Author: : mjg
Approved by: : ports-committers (lwhsu), khng
Differential revision: https://reviews.freebsd.org/D37074