ASoC: Intel: avs: Store pointer to link_stream in dma_data

ASoC: Intel: avs: Store pointer to link_stream in dma_data

While the HDAudio codec driver expectations must be met - store valid
pointer to HDAudio LINK stream in substream->runtime->private_data - the
code is more readable and easier to maintain if dma_data stores pointers
to both HOST and LINK stream.

DAI BE operations can refer to the LINK stream with data->link_stream,
similarly to how DAI FE operations access the HOST stream with
data->host_stream.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20240426095733.3946951-8-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>