ASoC: dt-bindings: spdif-dit: add missing sound-name-prefix property

This is used in meson-axg, meson-g12 and meson-gx. Add the property to
the binding.
This fixes the dtschema warning:
audio-codec-0: 'sound-name-prefix' does not match any of the
regexes: 'pinctrl-[0-9]+'

Signed-off-by: Alexander Stein <alexander.stein@mailbox.org>
Link: https://lore.kernel.org/r/20211223122434.39378-3-alexander.stein@mailbox.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/linux,spdif-dit.yaml

@@ -9,6 +9,9 @@ title: Dummy SPDIF Transmitter Device Tree Bindings
 maintainers:
   - Mark Brown <broonie@kernel.org>
 
+allOf:
+  - $ref: name-prefix.yaml#
+
 properties:
   compatible:
     const: linux,spdif-dit
@@ -16,6 +19,8 @@ properties:
   "#sound-dai-cells":
     const: 0
 
+  sound-name-prefix: true
+
 required:
   - "#sound-dai-cells"
   - compatible