ASoC: soc-dapm.h: fixup warning struct snd_pcm_substream not declared

ASoC: soc-dapm.h: fixup warning struct snd_pcm_substream not declared

[ Upstream commit 4941a23fb8216930728aca3fc657dcf1fa0b1d46 ]

Add struct snd_pcm_substream forward declaration

Fixes: 4428552673c6 ("ASoC: dapm: Only power up active channels from a DAI")
Signed-off-by: Lucas Tanure <lucas.tanure@collabora.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230215132851.1626881-1-lucas.tanure@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>