arm64: dts: mt6797: Fix mmsys node name

Node names are supposed to match the class of the device. The
mmsys node is a syscon as it provides more then just a clock controller.
Update the name.
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Reviewed-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20200518113156.25009-4-matthias.bgg@kernel.orgSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>

arch/arm64/boot/dts/mediatek/mt6797.dtsi

@@ -446,7 +446,7 @@ i2c5: i2c@1101c000 {
 		status = "disabled";
 	};
 
-	mmsys: mmsys_config@14000000 {
+	mmsys: syscon@14000000 {
 		compatible = "mediatek,mt6797-mmsys", "syscon";
 		reg = <0 0x14000000 0 0x1000>;
 		#clock-cells = <1>;