dt-bindings: input: touchscreen: ad7879: generic node names in example

Update example in ad7879 device tree documentation to use generic touch
controller node names.
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20191026090403.3057-3-marcel@ziswiler.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/ad7879.txt

@@ -38,7 +38,7 @@ Optional properties:
 
 Example:
 
-	ad7879@2c {
+	touchscreen0@2c {
 		compatible = "adi,ad7879-1";
 		reg = <0x2c>;
 		interrupt-parent = <&gpio1>;
@@ -52,7 +52,7 @@ Example:
 		adi,conversion-interval = /bits/ 8 <255>;
 	};
 
-	ad7879@1 {
+	touchscreen1@1 {
 		compatible = "adi,ad7879";
 		spi-max-frequency = <5000000>;
 		reg = <1>;