ASoC: soc-dai: add get_sdw_stream() callback

We only have a set() operation, provide the dual get() operation to
retrieve the stream information.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200225170041.23644-3-pierre-louis.bossart@linux.intel.com


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