dt-bindings: pwm: mxs-pwm: Increase #pwm-cells

We need to increase the pwm-cells for the optional flags parameter, in
order to implement support for polarity setting via DT.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

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

@@ -3,7 +3,7 @@ Freescale MXS PWM controller
 Required properties:
 - compatible: should be "fsl,imx23-pwm"
 - reg: physical base address and length of the controller's registers
-- #pwm-cells: should be 2. See pwm.yaml in this directory for a description of
+- #pwm-cells: should be 3. See pwm.yaml in this directory for a description of
   the cells format.
 - fsl,pwm-number: the number of PWM devices
 
@@ -12,6 +12,6 @@ Example:
 pwm: pwm@80064000 {
 	compatible = "fsl,imx28-pwm", "fsl,imx23-pwm";
 	reg = <0x80064000 0x2000>;
-	#pwm-cells = <2>;
+	#pwm-cells = <3>;
 	fsl,pwm-number = <8>;
 };