arm64: dts: mt8173: Fix mmsys node name

Node names are supposed to match the class of the device, mmsys is a
system controller (syscon) not a clock controller, so change the node
name accordingly.
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20200401201736.2980433-4-enric.balletbo@collabora.comSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>

arch/arm64/boot/dts/mediatek/mt8173.dtsi

@@ -922,7 +922,7 @@ u2port1: usb-phy@11291000 {
 			};
 		};
 
-		mmsys: clock-controller@14000000 {
+		mmsys: syscon@14000000 {
 			compatible = "mediatek,mt8173-mmsys", "syscon";
 			reg = <0 0x14000000 0 0x1000>;
 			power-domains = <&scpsys MT8173_POWER_DOMAIN_MM>;