arm64: dts: zx296718: set a better parent clock for I2S0

The default I2S0 parent clock AUDIO_24M can not be divided into required
sample rate in some cases, for example when 48KHz is needed.  Change the
parent clock to AUDIO_99M which works for most sample rates.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>