spi: stm32: 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/20191212135550.4634-10-peter.ujfalusi@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-stm32.c

@@ -1879,17 +1879,29 @@ static int stm32_spi_probe(struct platform_device *pdev)
 	master->transfer_one = stm32_spi_transfer_one;
 	master->unprepare_message = stm32_spi_unprepare_msg;
 
-	spi->dma_tx = dma_request_slave_channel(spi->dev, "tx");
-	if (!spi->dma_tx)
+	spi->dma_tx = dma_request_chan(spi->dev, "tx");
+	if (IS_ERR(spi->dma_tx)) {
+		ret = PTR_ERR(spi->dma_tx);
+		spi->dma_tx = NULL;
+		if (ret == -EPROBE_DEFER)
+			goto err_clk_disable;
+
 		dev_warn(&pdev->dev, "failed to request tx dma channel\n");
-	else
+	} else {
 		master->dma_tx = spi->dma_tx;
+	}
+
+	spi->dma_rx = dma_request_chan(spi->dev, "rx");
+	if (IS_ERR(spi->dma_rx)) {
+		ret = PTR_ERR(spi->dma_rx);
+		spi->dma_rx = NULL;
+		if (ret == -EPROBE_DEFER)
+			goto err_dma_release;
 
-	spi->dma_rx = dma_request_slave_channel(spi->dev, "rx");
-	if (!spi->dma_rx)
 		dev_warn(&pdev->dev, "failed to request rx dma channel\n");
-	else
+	} else {
 		master->dma_rx = spi->dma_rx;
+	}
 
 	if (spi->dma_tx || spi->dma_rx)
 		master->can_dma = stm32_spi_can_dma;
@@ -1901,26 +1913,26 @@ static int stm32_spi_probe(struct platform_device *pdev)
 	if (ret) {
 		dev_err(&pdev->dev, "spi master registration failed: %d\n",
 			ret);
-		goto err_dma_release;
+		goto err_pm_disable;
 	}
 
 	if (!master->cs_gpiods) {
 		dev_err(&pdev->dev, "no CS gpios available\n");
 		ret = -EINVAL;
-		goto err_dma_release;
+		goto err_pm_disable;
 	}
 
 	dev_info(&pdev->dev, "driver initialized\n");
 
 	return 0;
 
+err_pm_disable:
+	pm_runtime_disable(&pdev->dev);
 err_dma_release:
 	if (spi->dma_tx)
 		dma_release_channel(spi->dma_tx);
 	if (spi->dma_rx)
 		dma_release_channel(spi->dma_rx);
-
-	pm_runtime_disable(&pdev->dev);
 err_clk_disable:
 	clk_disable_unprepare(spi->clk);
 err_master_put: