acp-dma: clear channel pointer after free on probe failure

On a partial channel-init failure the channel array was freed but the
pointer was left set, so a later probe retry would free it again. Clear
the pointer after freeing.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

src/drivers/amd/common/acp_dma.c

@@ -314,6 +314,7 @@ static int acp_dma_probe(struct dma *dma)
 				   sizeof(struct acp_dma_chan_data));
 		if (!acp_dma_chan) {
 			rfree(dma->chan);
+			dma->chan = NULL;
 			tr_err(&acpdma_tr, "acp-dma: %d channel %d private data alloc failed",
 			       dma->plat_data.id, channel);
 			return -ENOMEM;