ASoC: dt-bindings: max98088: add external clock binding

Allow setting the clock provider for the external clock called "mclk".
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/maxim,max98088.txt

@@ -7,9 +7,17 @@ Required properties:
 - compatible: "maxim,max98088" or "maxim,max98089".
 - reg: The I2C address of the device.
 
+Optional properties:
+
+- clocks: the clock provider of MCLK, see ../clock/clock-bindings.txt section
+  "consumer" for more information.
+- clock-names: must be set to "mclk"
+
 Example:
 
 max98089: codec@10 {
 	compatible = "maxim,max98089";
 	reg = <0x10>;
+	clocks = <&clks IMX6QDL_CLK_CKO2>;
+	clock-names = "mclk";
 };