staging: vboxvideo: Replace crtc_helper enable/disable functions

Replace vbox_crtc_commit and vbox_crtc_disable with
vbox_crtc_atomic_[en|dis]able which are the preferred callbacks for
these for atomic drivers.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>