ASoC: fsl_esai: Remove unused 'imx' field

The 'imx' field is not used anywhere, so get rid of it.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Shengjiu Wang <shengjiu.wang@gmail.com>
Link: https://lore.kernel.org/r/20210206142753.536459-1-festevam@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>