ASoC: rt5677: fixed wrong DMIC ref clock

DMIC clock source is not from codec system clock directly. it is
generated from the division of system clock. And it should be 256 *
sample rate of AIF1.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org