mips: dts: realtek: Replace uart clock property

Add a fixed clock to define the clock frequency of the Lexra bus and use
this for the two uart nodes instead of a separate clock-frequency
property.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/dts/realtek/rtl838x.dtsi

@@ -34,6 +34,12 @@
 		interrupt-controller;
 	};
 
+	lx_clk: clock-lexra {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <200000000>;
+	};
+
 	soc@18000000 {
 		compatible = "simple-bus";
 		#address-cells = <1>;
@@ -44,7 +50,7 @@
 			compatible = "ns16550a";
 			reg = <0x2000 0x100>;
 
-			clock-frequency = <200000000>;
+			clocks = <&lx_clk>;
 
 			interrupt-parent = <&intc>;
 			interrupts = <31>;
@@ -61,7 +67,7 @@
 			compatible = "ns16550a";
 			reg = <0x2100 0x100>;
 
-			clock-frequency = <200000000>;
+			clocks = <&lx_clk>;
 
 			interrupt-parent = <&intc>;
 			interrupts = <30>;