ASoC: rockchip: add missing slave_config setting for I2S

This patch adds missing prepare_sleve_config that is needed for
setup the DMA slave channel for I2S.
Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/rockchip/rockchip_pcm.c

@@ -33,6 +33,7 @@ static const struct snd_pcm_hardware snd_rockchip_hardware = {
 
 static const struct snd_dmaengine_pcm_config rk_dmaengine_pcm_config = {
 	.pcm_hardware = &snd_rockchip_hardware,
+	.prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config,
 	.prealloc_buffer_size = 32 * 1024,
 };