regulator: pwm-regulator: fix example syntax

The "Continuous Voltage" example specifies a pwm-dutycycle-range.
However, an equal sign is missing between the property name and value.
Fix this to allow copy and paste from the documentation when writing an
own .dts file with a pwm-regulator.

Signed-off-by: Martin Blumenstingl <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/regulator/pwm-regulator.txt

···
 		 * Inverted PWM logic, and the duty cycle range is limited
 		 * to 30%-70%.
 		 */
-		pwm-dutycycle-range <700 300>; /* */
+		pwm-dutycycle-range = <700 300>; /* */
 	};
 
 Voltage Table Example: