ASoC: dt-bindings: realtek,rt5616: document mclk clock

ASoC: dt-bindings: realtek,rt5616: document mclk clock

Both devicetrees and driver implementation already use the specified mclk
in the field, so at least document the clock too, similarly to other
Realtek codec.

This has the nice additional effect of getting rid of dtbscheck warning.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20240830203819.1972536-2-heiko@sntech.de
Signed-off-by: Mark Brown <broonie@kernel.org>