i2c: i2c-cbus-gpio: Add vendor prefix to retu node in example

The example contains a device node for a retu device, but
its compatible string doesn't have a vendor prefix.

While being there, drop the -mfd suffix since isn't correct.

Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/i2c/i2c-cbus-gpio.txt

@@ -20,8 +20,8 @@ i2c@0 {
 	#address-cells = <1>;
 	#size-cells = <0>;
 
-	retu-mfd: retu@1 {
-		compatible = "retu-mfd";
+	retu: retu@1 {
+		compatible = "nokia,retu";
 		reg = <0x1>;
 	};
 };