ASoC: dt-bindings: fsl,audmix: make 'dais' property to be optional

Make 'dais' property to be optional. When there is no 'dais' property,
driver won't register the card, dts should have audio graph card node
for linking this device.

Signed-off-by: Shengjiu Wang <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/fsl,audmix.yaml

···
   - clocks
   - clock-names
   - power-domains
-  - dais
 
 unevaluatedProperties: false