ASoC: fsl_audmix: remove "model" attribute

Use "of_device_id.data" to specify the machine driver
instead of "model" DTS attribute.

Signed-off-by: Viorel Suman <viorel.suman@nxp.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>