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/output.c b/drivers/video/omap2/dss/output.c
index 0ba168e..3f5c0a7 100644
--- a/drivers/video/omap2/dss/output.c
+++ b/drivers/video/omap2/dss/output.c
@@ -146,7 +146,13 @@
 
 struct omap_dss_device *omapdss_find_output_from_display(struct omap_dss_device *dssdev)
 {
-	return omap_dss_get_device(dssdev->output);
+	while (dssdev->output)
+		dssdev = dssdev->output;
+
+	if (dssdev->id != 0)
+		return omap_dss_get_device(dssdev);
+
+	return NULL;
 }
 EXPORT_SYMBOL(omapdss_find_output_from_display);