ASoC: dt-bindings: renesas,rsnd: add missing renesas,rcar_sound-gen4

It is missing generic compatible for R-Car Gen4
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/8734rrcewo.wl-kuninori.morimoto.gx@renesas.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/renesas,rsnd.yaml

@@ -56,6 +56,7 @@ properties:
           - renesas,rcar_sound-gen1
           - renesas,rcar_sound-gen2
           - renesas,rcar_sound-gen3
+          - renesas,rcar_sound-gen4
 
   reg:
     minItems: 1