drm/omap: use dispc_channel_connected in output drivers

Use 'out->dispc_channel_connected' to check if the device is connected
to an overlay manager or not, instead of using 'out->manager'.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/dss/rfbi.c

@@ -880,7 +880,7 @@ static int rfbi_display_enable(struct omap_dss_device *dssdev)
 	struct omap_dss_device *out = &rfbi.output;
 	int r;
 
-	if (out->manager == NULL) {
+	if (!out->dispc_channel_connected) {
 		DSSERR("failed to enable display: no output/manager\n");
 		return -ENODEV;
 	}