OMAPDSS: APPLY: fix NULL pointer deref when mgr is not set

extra_info_update_ongoing() goes through all overlays, but doesn't check
if the overlay is connected to a manager. This leads to a crash whenever
an overlay has been detached.

Add a check to skip the non-connected overlays.
Reported-by: Rob Clark <rob@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/dss/apply.c

@@ -327,6 +327,9 @@ static bool extra_info_update_ongoing(void)
 		ovl = omap_dss_get_overlay(i);
 		op = get_ovl_priv(ovl);
 
+		if (!ovl->manager)
+			continue;
+
 		mp = get_mgr_priv(ovl->manager);
 
 		if (!mp->enabled)