emulators/virtualbox-ose-additions: Fix vboxvfs panic
Fix panic on mount when trying to use vbox VFS after
base r355790 (or git commit hash 6fa079fc3f5e).
PR: 255208
MFH: 2021Q2
(cherry picked from commit 8a311de0cb804d8b135413884b4fb336d287ad5a)