ASoC: rl6231: Modify the target DMIC clock rate

Some DMIC components will not work correctly in the clock rate 3.072MHz.
We recommend the clock rate 1.536MHz in the gerenal case.

Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Link: https://lore.kernel.org/r/20200604071016.3981-1-oder_chiou@realtek.com
Signed-off-by: Mark Brown <broonie@kernel.org>