ASoC: intel: sof_sdw: Move sdw_pin_index into private struct

ASoC: intel: sof_sdw: Move sdw_pin_index into private struct

Whilst it should not cause any issues as only a single instance of the
machine will be instantiated, it is still slightly better practice to
keep working data in the private data structure, rather than a global
variable. Move sdw_pin_index into the mc_private structure.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20230915075611.1619548-2-yung-chuan.liao@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>