ARM: dts: rockchip: add "rockchip,rk3228-grf" compatible for rk322x grf node

rockchip,rk3228-grf is used both for rk3228 and rk3229.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk322x.dtsi

@@ -233,7 +233,7 @@ i2s2: i2s2@100e0000 {
 	};
 
 	grf: syscon@11000000 {
-		compatible = "syscon", "simple-mfd";
+		compatible = "rockchip,rk3228-grf", "syscon", "simple-mfd";
 		reg = <0x11000000 0x1000>;
 		#address-cells = <1>;
 		#size-cells = <1>;