ASoC: rt5670: remove unused mux/mixer define

Some mux/mixer are not used. Remove them from the driver.

Signed-off-by: Bard liao <yung-chuan.liao@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>