devicetree: pwm: mxs-pwm.txt: Fix reg field annotation

In the reg field we should annotate the register address space in hexadecimal
format.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

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

@@ -11,7 +11,7 @@ Example:
 
 pwm: pwm@80064000 {
 	compatible = "fsl,imx28-pwm", "fsl,imx23-pwm";
-	reg = <0x80064000 2000>;
+	reg = <0x80064000 0x2000>;
 	#pwm-cells = <2>;
 	fsl,pwm-number = <8>;
 };