drm/fb_cma_helper: do not free fbdev if there is none

If fbdev emulation is not in use (or not built-in), fb_helper.fbdev
is NULL. Don't call calling drm_fbdev_cma_defio_fini in this case.
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161020003221.2941-2-stefan@agner.ch

drivers/gpu/drm/drm_fb_cma_helper.c

@@ -560,7 +560,8 @@ EXPORT_SYMBOL_GPL(drm_fbdev_cma_init);
 void drm_fbdev_cma_fini(struct drm_fbdev_cma *fbdev_cma)
 {
 	drm_fb_helper_unregister_fbi(&fbdev_cma->fb_helper);
-	drm_fbdev_cma_defio_fini(fbdev_cma->fb_helper.fbdev);
+	if (fbdev_cma->fb_helper.fbdev)
+		drm_fbdev_cma_defio_fini(fbdev_cma->fb_helper.fbdev);
 	drm_fb_helper_release_fbi(&fbdev_cma->fb_helper);
 
 	if (fbdev_cma->fb) {