ASoC: Intel: bytcr-rt5640: fix settings in internal clock mode

Frequency value of zero did not make sense, use same 24.576MHz
setting and only change the clock source in idle mode

Suggested-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>