dt-bindings: hwmon: adi,ltc2992: correct unit address in example

lower-case hex is expected for unit addresses:

  adi,ltc2992.example.dts:22.24-38.15: Warning (i2c_bus_reg): /example-0/i2c/ltc2992@6F: I2C bus unit address format error, expected "6f"
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230118172237.349111-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/adi,ltc2992.yaml

@@ -59,12 +59,12 @@ examples:
         #address-cells = <1>;
         #size-cells = <0>;
 
-        ltc2992@6F {
+        ltc2992@6f {
                 #address-cells = <1>;
                 #size-cells = <0>;
 
                 compatible = "adi,ltc2992";
-                reg = <0x6F>;
+                reg = <0x6f>;
 
                 channel@0 {
                         reg = <0x0>;