gtkglwidget: fix build error cause by api change in base-gl

commit 908c6c5d422ab069b5e642b06e536be2afea1816
Author: Haihua Hu <jared.hu@nxp.com>
Date:   Thu Apr 12 16:22:25 2018 +0800

    gloverlaycompositor: add subtitle rotate support follow video

    upstream status: Pending
    https://bugzilla.gnome.org/show_bug.cgi?id=790470

upsteam status: imx specific
diff --git a/ext/gtk/gtkgstglwidget.c b/ext/gtk/gtkgstglwidget.c
index 76c46c9..bf56587 100644
--- a/ext/gtk/gtkgstglwidget.c
+++ b/ext/gtk/gtkgstglwidget.c
@@ -278,7 +278,7 @@
       base_widget->buffer, context);
 
   _redraw_texture (GTK_GST_GL_WIDGET (widget), priv->current_tex);
-  gst_gl_overlay_compositor_draw_overlays (priv->overlay_compositor);
+  gst_gl_overlay_compositor_draw_overlays (priv->overlay_compositor, NULL);
 
   gst_gl_insert_debug_marker (priv->other_context, "texture %u redrawn",
       priv->current_tex);