staging/vboxvideo: Use gem_free_object_unlocked

vboxvideo doesn't use dev->struct_mutex and therefore has no need to use
gem_free_object.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Michael Thayer <michael.thayer@oracle.com>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180327082356.24516-1-daniel.vetter@ffwll.ch

drivers/staging/vboxvideo/vbox_drv.c

@@ -242,7 +242,7 @@ static struct drm_driver driver = {
 	.minor = DRIVER_MINOR,
 	.patchlevel = DRIVER_PATCHLEVEL,
 
-	.gem_free_object = vbox_gem_free_object,
+	.gem_free_object_unlocked = vbox_gem_free_object,
 	.dumb_create = vbox_dumb_create,
 	.dumb_map_offset = vbox_dumb_mmap_offset,
 	.dumb_destroy = drm_gem_dumb_destroy,