ASoC: sgtl5000: Pass the required '#sound-dai-cells'

DTC now warns about missing #sound-dai-cells:

arch/arm/boot/dts/imx6ul-geam.dtb: Warning (sound_dai_property): /sound/simple-audio-card,codec: Missing property '#sound-dai-cells' in node /soc/aips-bus@2100000/i2c@21a0000/codec@a or bad phandle (referred from sound-dai[0])

Pass the required '#sound-dai-cells' property to improve the documentation.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/sgtl5000.txt

@@ -5,6 +5,8 @@ Required properties:
 
 - reg : the I2C address of the device
 
+- #sound-dai-cells: must be equal to 0
+
 - clocks : the clock provider of SYS_MCLK
 
 - VDDA-supply : the regulator provider of VDDA
@@ -40,6 +42,7 @@ Example:
 codec: sgtl5000@a {
 	compatible = "fsl,sgtl5000";
 	reg = <0x0a>;
+	#sound-dai-cells = <0>;
 	clocks = <&clks 150>;
 	micbias-resistor-k-ohms = <2>;
 	micbias-voltage-m-volts = <2250>;