OMAPDSS: fix bogus WARN_ON in dss_runtime_put()

pm_runtime_put_sync() in dss_runtime_put() returns -EBUSY when any child
of dss is still enabled. This happens, for example, when a display
output is enabled and one dumps the clocks via debugfs. This causes
dss_runtime_get & put to be called.

While I couldn't find anything about this in the documentation and it
wasn't immediately clear from runtime_pm code, it looks to me that
pm_runtime_put_sync() returns -EBUSY to inform that things went fine,
but the device could not be turned off as there are still child devices
that are enabled. This is not a problem.

This patch skips the WARN_ON if pm_runtime_put_sync() returns -EBUSY.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/dss/dss.c

@@ -731,7 +731,7 @@ static void dss_runtime_put(void)
 	DSSDBG("dss_runtime_put\n");
 
 	r = pm_runtime_put_sync(&dss.pdev->dev);
-	WARN_ON(r < 0);
+	WARN_ON(r < 0 && r != -EBUSY);
 }
 
 /* DEBUGFS */