rockchip: rock2: dts: use status = "okay" not ok

u-boot only recognize okay to enable a node (Linux seems to be more
lenient here). So use okay instead.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/dts/rk3288-rock2-square.dts

@@ -111,7 +111,7 @@
 };
 
 &gmac {
-	status = "ok";
+	status = "okay";
 };
 
 &hdmi {