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 <[e-mail]>
Signed-off-by: Alexandre Belloni <[e-mail]>

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

···
 	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>;