dt-bindings: rtc: use a generic node name for ds1307

The example should follow the practice or using a generic node name
instead of the precise programming model, as recommended by the DTSpec.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/rtc-ds1307.txt

@@ -35,7 +35,7 @@ Optional properties:
 	Should be given if internal trickle charger diode should be disabled
 
 Example:
-	rtc1: ds1339@68 {
+	ds1339: rtc@68 {
 		compatible = "dallas,ds1339";
 		reg = <0x68>;
 		interrupt-parent = <&gpio4>;