mmc: dw_mmc: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20191217112656.30860-1-peter.ujfalusi@ti.comSigned-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -833,12 +833,14 @@ static int dw_mci_edmac_init(struct dw_mci *host)
 	if (!host->dms)
 		return -ENOMEM;
 
-	host->dms->ch = dma_request_slave_channel(host->dev, "rx-tx");
-	if (!host->dms->ch) {
+	host->dms->ch = dma_request_chan(host->dev, "rx-tx");
+	if (IS_ERR(host->dms->ch)) {
+		int ret = PTR_ERR(host->dms->ch);
+
 		dev_err(host->dev, "Failed to get external DMA channel.\n");
 		kfree(host->dms);
 		host->dms = NULL;
-		return -ENXIO;
+		return ret;
 	}
 
 	return 0;