MIPS: Use lower case for addresses in nexys4ddr.dts

DTC introduced an i2c_bus_reg check in v1.4.7, used since Linux v4.20,
which complains about upper case addresses used in the unit name.

nexys4ddr.dts names an I2C device node "ad7420@4B", leading to:

  arch/mips/boot/dts/xilfpga/nexys4ddr.dts:109.16-112.8: Warning
    (i2c_bus_reg): /i2c@10A00000/ad7420@4B: I2C bus unit address format
    error, expected "4b"

Fix this by switching to lower case addresses throughout the file, as is
*mostly* the case in the file already & fairly standard throughout the
tree.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: stable@vger.kernel.org # v4.20+
Cc: linux-mips@vger.kernel.org

arch/mips/boot/dts/xilfpga/nexys4ddr.dts

@@ -90,11 +90,11 @@ axi_uart16550: serial@10400000 {
 		interrupts = <0>;
 	};
 
-	axi_i2c: i2c@10A00000 {
+	axi_i2c: i2c@10a00000 {
 	    compatible = "xlnx,xps-iic-2.00.a";
 	    interrupt-parent = <&axi_intc>;
 	    interrupts = <4>;
-	    reg = < 0x10A00000 0x10000 >;
+	    reg = < 0x10a00000 0x10000 >;
 	    clocks = <&ext>;
 	    xlnx,clk-freq = <0x5f5e100>;
 	    xlnx,family = "Artix7";
@@ -106,9 +106,9 @@ axi_i2c: i2c@10A00000 {
 	    #address-cells = <1>;
 	    #size-cells = <0>;
 
-	    ad7420@4B {
+	    ad7420@4b {
 		compatible = "adi,adt7420";
-		reg = <0x4B>;
+		reg = <0x4b>;
 	    };
 	} ;
 };