ASoC: dt-bindings: sgtl5000: Add common clock properties

Add common properties appearing in DTSes (assigned-clocks and similar)
to fix dtbs_check warnings like:

  arch/arm64/boot/dts/freescale/imx8mq-librem5-devkit.dt.yaml: audio-codec@a:
    'assigned-clock-parents', 'assigned-clock-rates', 'assigned-clocks' do not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200925212719.23286-1-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/sgtl5000.yaml

@@ -19,6 +19,10 @@ properties:
   "#sound-dai-cells":
     const: 0
 
+  assigned-clock-parents: true
+  assigned-clock-rates: true
+  assigned-clocks: true
+
   clocks:
     items:
       - description: the clock provider of SYS_MCLK