ASoC: Use inline function for type safety in snd_soc_substream_to_rtd()

ASoC: Use inline function for type safety in snd_soc_substream_to_rtd()

A common pattern in sound drivers is getting 'struct snd_soc_pcm_runtime'
from 'struct snd_pcm_substream' opaque pointer private_data field with
snd_soc_substream_to_rtd().  However 'private_data' appears in several
other structures as well, including 'struct snd_compr_stream'.  The
field might not hold the same type for every structure, although seems
the case at least for 'struct snd_compr_stream', so code can easily make
a mistake by using macro for wrong structure passed as argument.

Switch from macro to inline function, so such mistake will be build-time
detectable.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240501175127.34301-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>