arm64: dts: verdin-imx8mm: fix dev board audio playback

Set optional `simple-audio-card,mclk-fs` parameter to ensure a proper
clock to the nau8822 audio codec. Without this change with an audio
stream rate of 44.1 kHz the playback is faster.
Set the MCLK at the right frequency, codec can properly use it to
generate 44.1 kHz I2S-FS.

Fixes: 6a57f224 ("arm64: dts: freescale: add initial support for verdin imx8m mini")
Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>