mmc: mxs: 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: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20191217112847.31351-1-peter.ujfalusi@ti.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/mxs-mmc.c

@@ -623,11 +623,11 @@ static int mxs_mmc_probe(struct platform_device *pdev)
 		goto out_clk_disable;
 	}
 
-	ssp->dmach = dma_request_slave_channel(&pdev->dev, "rx-tx");
-	if (!ssp->dmach) {
+	ssp->dmach = dma_request_chan(&pdev->dev, "rx-tx");
+	if (IS_ERR(ssp->dmach)) {
 		dev_err(mmc_dev(host->mmc),
 			"%s: failed to request dma\n", __func__);
-		ret = -ENODEV;
+		ret = PTR_ERR(ssp->dmach);
 		goto out_clk_disable;
 	}