ASoC: Intel: avs: Initialize private data for subsequent HDA FEs

ASoC: Intel: avs: Initialize private data for subsequent HDA FEs

HDAudio implementation found in sound/pci/hda expects a valid stream
pointer in substream->runtime->private_data location. For ASoC users,
that should point to a valid link stream which is assigned when BE
opens.

As BE borrows its runtime from FE, the information may be lost when
reparenting comes into picture - see dpcm_be_reparent(). To support the
DPCM reparenting functionality for HDAudio scenarios while still
fulfilling expectations of HDAudio common code, have all FEs point to
the same private data.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20221118113052.1340593-1-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>