soundwire: Use snd_soc_substream_to_rtd() to obtain rtd

Utilize the helper function instead of casting from ->private_data
directly.
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20240219105206.335738-1-cezary.rojewski@intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/stream.c

@@ -1718,7 +1718,7 @@ EXPORT_SYMBOL(sdw_deprepare_stream);
 static int set_stream(struct snd_pcm_substream *substream,
 		      struct sdw_stream_runtime *sdw_stream)
 {
-	struct snd_soc_pcm_runtime *rtd = substream->private_data;
+	struct snd_soc_pcm_runtime *rtd = snd_soc_substream_to_rtd(substream);
 	struct snd_soc_dai *dai;
 	int ret = 0;
 	int i;
@@ -1771,7 +1771,7 @@ EXPORT_SYMBOL(sdw_alloc_stream);
 int sdw_startup_stream(void *sdw_substream)
 {
 	struct snd_pcm_substream *substream = sdw_substream;
-	struct snd_soc_pcm_runtime *rtd = substream->private_data;
+	struct snd_soc_pcm_runtime *rtd = snd_soc_substream_to_rtd(substream);
 	struct sdw_stream_runtime *sdw_stream;
 	char *name;
 	int ret;
@@ -1815,7 +1815,7 @@ EXPORT_SYMBOL(sdw_startup_stream);
 void sdw_shutdown_stream(void *sdw_substream)
 {
 	struct snd_pcm_substream *substream = sdw_substream;
-	struct snd_soc_pcm_runtime *rtd = substream->private_data;
+	struct snd_soc_pcm_runtime *rtd = snd_soc_substream_to_rtd(substream);
 	struct sdw_stream_runtime *sdw_stream;
 	struct snd_soc_dai *dai;