OMAPDSS: modify get/find functions to go through the device chain

In the future will have arbitrarily long video pipeline chains, instead
of the current two-entities-per-pipeline model.

This patch changes the affected get/find style functions so that they
properly go through the video pipeline chain, for example when getting
the overlay manager connected to a given display.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/apply.c b/drivers/video/omap2/dss/apply.c
index 752b985..d6212d63 100644
--- a/drivers/video/omap2/dss/apply.c
+++ b/drivers/video/omap2/dss/apply.c
@@ -422,7 +422,19 @@
 
 static struct omap_dss_device *dss_mgr_get_device(struct omap_overlay_manager *mgr)
 {
-	return mgr->output ? mgr->output->device : NULL;
+	struct omap_dss_device *dssdev;
+
+	dssdev = mgr->output;
+	if (dssdev == NULL)
+		return NULL;
+
+	while (dssdev->device)
+		dssdev = dssdev->device;
+
+	if (dssdev->driver)
+		return dssdev;
+	else
+		return NULL;
 }
 
 static struct omap_dss_device *dss_ovl_get_device(struct omap_overlay *ovl)