of/unittest: Fix I2C bus unit-address error

dtc has new checks for I2C buses. Fix the warnings in unit-addresses in
the unittests.

drivers/of/unittest-data/testcases.dtb: Warning (i2c_bus_reg): /testcase-data/overlay-node/test-bus/i2c-test-bus/test-unittest14/i2c@0/test-mux-dev: I2C bus unit address format error, expected "20"
drivers/of/unittest-data/overlay_15.dtb: Warning (i2c_bus_reg): /fragment@0/__overlay__/test-unittest15/i2c@0/test-mux-dev: I2C bus unit address format error, expected "20"

Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/unittest-data/overlay_15.dts

@@ -20,8 +20,8 @@
 			#size-cells = <0>;
 			reg = <0>;
 
-			test-mux-dev {
-				reg = <32>;
+			test-mux-dev@20 {
+				reg = <0x20>;
 				compatible = "unittest-i2c-dev";
 				status = "okay";
 			};

drivers/of/unittest-data/tests-overlay.dtsi

@@ -103,8 +103,8 @@
 							#size-cells = <0>;
 							reg = <0>;
 
-							test-mux-dev {
-								reg = <32>;
+							test-mux-dev@20 {
+								reg = <0x20>;
 								compatible = "unittest-i2c-dev";
 								status = "okay";
 							};