ASoC: dmaengine: Restore NULL prepare_slave_config() callback

As pointed out by Sascha Hauer, this patch changes:
if (pmc->config && !pcm->config->prepare_slave_config)
        <do nothing>
to:
if (pmc->config && !pcm->config->prepare_slave_config)
        snd_dmaengine_pcm_prepare_slave_config()

This breaks the drivers that do not need a call to
dmaengine_slave_config(). Drivers that still need to call
snd_dmaengine_pcm_prepare_slave_config(), but have a NULL
pcm->config->prepare_slave_config should use
snd_dmaengine_pcm_prepare_slave_config() as their prepare_slave_config
callback.

Fixes: 9a1e1344 ("ASoC: dmaengine: do not use a NULL prepare_slave_config() callback")
Reported-by: Sascha Hauer <sha@pengutronix.de>
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Link: https://lore.kernel.org/r/20220421125403.2180824-1-codrin.ciubotariu@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-generic-dmaengine-pcm.c

@@ -86,10 +86,10 @@ static int dmaengine_pcm_hw_params(struct snd_soc_component *component,
 
 	memset(&slave_config, 0, sizeof(slave_config));
 
-	if (pcm->config && pcm->config->prepare_slave_config)
-		prepare_slave_config = pcm->config->prepare_slave_config;
-	else
+	if (!pcm->config)
 		prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
+	else
+		prepare_slave_config = pcm->config->prepare_slave_config;
 
 	if (prepare_slave_config) {
 		int ret = prepare_slave_config(substream, params, &slave_config);