ASoC: Constify return of snd_soc_dai_get_pcm_stream()

Returned 'struct snd_soc_pcm_stream' by snd_soc_dai_get_pcm_stream() is
not modified by the users, so it can be changed as pointer to const.
This is a necessary step towards making the 'dai->driver' a pointer to
const.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://msgid.link/r/20240617-n-asoc-const-auto-selectable-formats-v1-5-8004f346ee38@linaro.org


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