glx: Make sure we get an FBConfig the root window's visual.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Keith Packard <keithp@keithp.com>

hw/kdrive/ephyr/ephyr_glamor_glx.c

@@ -313,6 +313,7 @@ ephyr_glamor_get_visual(void)
         GLX_GREEN_SIZE, 1,
         GLX_BLUE_SIZE, 1,
         GLX_DOUBLEBUFFER, 1,
+        GLX_VISUAL_ID, DefaultVisual(dpy, DefaultScreen(dpy)),
         None
     };
     int event_base = 0, error_base = 0, nelements;