dt-bindings: pwm: mxs: Document the clocks property

The 'clocks' property is mandatory for the PWM to operate.

Document it.
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

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

@@ -25,6 +25,9 @@ properties:
   reg:
     maxItems: 1
 
+  clocks:
+    maxItems: 1
+
   "#pwm-cells":
     const: 3
 
@@ -35,6 +38,7 @@ properties:
 required:
   - compatible
   - reg
+  - clocks
   - fsl,pwm-number
 
 additionalProperties: false
@@ -44,6 +48,7 @@ examples:
     pwm@80064000 {
         compatible = "fsl,imx23-pwm";
         reg = <0x80064000 0x2000>;
+        clocks = <&clks 30>;
         #pwm-cells = <3>;
         fsl,pwm-number = <8>;
     };