ASoC: intel: sof_sdw: add .exit callback function

We may allocate some resources in sof_sdw_codec_info .init function.
Adding a corresponding .exit function can help to release these resources.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20200820134542.8682-1-yung-chuan.liao@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>