ASoC: rockchip: Update description of rockchip, codec

Update description for newly added optional audio codecs.

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rockchip,rk3399-gru-sound.txt

@@ -4,7 +4,7 @@ Required properties:
 - compatible: "rockchip,rk3399-gru-sound"
 - rockchip,cpu: The phandle of the Rockchip I2S controller that's
   connected to the codecs
-- rockchip,codec: The phandle of the MAX98357A/RT5514/DA7219 codecs
+- rockchip,codec: The phandle of the audio codecs
 
 Optional properties:
 - dmic-wakeup-delay-ms : specify delay time (ms) for DMIC ready.