mfd: madera: Update DT binding document to support clock supplies

Add the 3 input clock sources for the chip into the device tree binding
document.
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/madera.txt

@@ -67,6 +67,14 @@ Optional properties:
     As defined in bindings/gpio.txt.
     Although optional, it is strongly recommended to use a hardware reset
 
+  - clocks: Should reference the clocks supplied on MCLK1, MCLK2 and MCLK3
+  - clock-names: May contain up to three strings:
+      "mclk1" for the clock supplied on MCLK1, recommended to be a high
+      quality audio reference clock
+      "mclk2" for the clock supplied on MCLK2, required to be an always on
+      32k clock
+      "mclk3" for the clock supplied on MCLK3
+
   - MICBIASx : Initial data for the MICBIAS regulators, as covered in
     Documentation/devicetree/bindings/regulator/regulator.txt.
     One for each MICBIAS generator (MICBIAS1, MICBIAS2, ...)