dts: usb-c: fix invalid power-role in example

The example sets the power-role to "SINK", but the value is
case-sensitive and only accepts lowercase "sink".

Signed-off-by: Jonas Otto <[email protected]>

Author: ottojo

dts/bindings/usb-c/usb-c-connector.yaml

@@ -29,7 +29,7 @@ description: |
             reg = <1>;
             tcpc = <&ucpd1>;
             vbus = <&vbus1>;
-            power-role = "SINK";
+            power-role = "sink";
             sink-pdos = <PDO_FIXED(5000, 2000, PDO_FIXED_USB_COMM)
                          PDO_VAR(5000, 12000, 2000)>;
             op-sink-microwatt = <10000000>;