gma500: Fix leak of uncached page

This was reported a long time ago (and I apologize to whoever it was that
reported it as I've lost the original report).

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/gma500/psb_drv.c

@@ -246,6 +246,7 @@ static int psb_driver_unload(struct drm_device *dev)
 		}
 		psb_gtt_takedown(dev);
 		if (dev_priv->scratch_page) {
+			set_pages_wb(dev_priv->scratch_page, 1);
 			__free_page(dev_priv->scratch_page);
 			dev_priv->scratch_page = NULL;
 		}