ASoC: rsnd: set dmaen->chan = NULL when error case

rsnd_dmaen_quit() is assuming dmaen->chan is NULL if it failed
to get DMAEngine channel. but, current dmaen->chan might have
error value when error case (this driver is checking it by IS_ERR_OR_NULL())
This patch makes sure dmaen->chan is NULL when error case.
Otherwise, it will contact to unknown address in rsnd_dmaen_quit()

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rcar/dma.c

@@ -156,6 +156,7 @@ static int rsnd_dmaen_init(struct rsnd_priv *priv, struct rsnd_dma *dma, int id,
 						  (void *)id);
 	}
 	if (IS_ERR_OR_NULL(dmaen->chan)) {
+		dmaen->chan = NULL;
 		dev_err(dev, "can't get dma channel\n");
 		goto rsnd_dma_channel_err;
 	}