ASoC: meson: t9015: add missing sound-name-prefix property

This is used in meson-gxl and meson-g12-common .dtsi. Add the property to
the binding.
This fixes the dtschema warning:
audio-controller@32000: 'sound-name-prefix' does not match any of the
regexes: 'pinctrl-[0-9]+'

Signed-off-by: Alexander Stein <alexander.stein@mailbox.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211218143423.18768-2-alexander.stein@mailbox.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/amlogic,t9015.yaml

@@ -9,6 +9,9 @@ title: Amlogic T9015 Internal Audio DAC
 maintainers:
   - Jerome Brunet <jbrunet@baylibre.com>
 
+allOf:
+  - $ref: name-prefix.yaml#
+
 properties:
   $nodename:
     pattern: "^audio-controller@.*"
@@ -38,6 +41,8 @@ properties:
     description:
       Analogue power supply.
 
+  sound-name-prefix: true
+
 required:
   - "#sound-dai-cells"
   - compatible