OMAP: DSS2: move get_resolution()

Move get_resolution() from omap_dss_device to omap_dss_driver.

This is part of a larger patch-set, which moves the control from omapdss
driver to the display driver.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>
diff --git a/drivers/video/omap2/dss/overlay.c b/drivers/video/omap2/dss/overlay.c
index b7f9a73..0c5bea2 100644
--- a/drivers/video/omap2/dss/overlay.c
+++ b/drivers/video/omap2/dss/overlay.c
@@ -350,7 +350,7 @@
 		return -EINVAL;
 	}
 
-	dssdev->get_resolution(dssdev, &dw, &dh);
+	dssdev->driver->get_resolution(dssdev, &dw, &dh);
 
 	DSSDBG("check_overlay %d: (%d,%d %dx%d -> %dx%d) disp (%dx%d)\n",
 			ovl->id,