ASoC: dt-bindings: renesas,rsnd: correct reg-names for R-Car Gen1

The device at 0xffd90000 is named SRU, both in the datasheet and SoC
DTSI. Fix the typo in the bindings to avoid the false positive report:

  sound@ffd90000: reg-names:0: 'sru' is not one of ['scu', 'ssi', 'adg']

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20240926113241.24060-2-wsa+renesas@sang-engineering.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Wolfram Sang

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

@@ -302,7 +302,7 @@ allOf:
         reg-names:
           items:
             enum:
-              - scu
+              - sru
               - ssi
               - adg
   # for Gen2/Gen3