staging: vboxvideo: make a couple of funcs static

Fix Sparse warnings:
drivers/staging/vboxvideo/vbox_mode.c:309:6: warning:
symbol 'vbox_primary_atomic_disable' was not declared. Should it be static?

drivers/staging/vboxvideo/vbox_mode.c:452:6: warning:
symbol 'vbox_cursor_atomic_disable' was not declared. Should it be static?

Signed-off-by: Craig Kewley <[e-mail]>
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/vboxvideo/vbox_mode.c

···
 				    plane->state->src_y >> 16);
 }
 
-void vbox_primary_atomic_disable(struct drm_plane *plane,
-				 struct drm_plane_state *old_state)
+static void vbox_primary_atomic_disable(struct drm_plane *plane,
+					struct drm_plane_state *old_state)
 {
 	struct drm_crtc *crtc = old_state->crtc;
 
···
 	mutex_unlock(&vbox->hw_mutex);
 }
 
-void vbox_cursor_atomic_disable(struct drm_plane *plane,
-				struct drm_plane_state *old_state)
+static void vbox_cursor_atomic_disable(struct drm_plane *plane,
+				       struct drm_plane_state *old_state)
 {
 	struct vbox_private *vbox =
 		container_of(plane->dev, struct vbox_private, ddev);