media: stm32-dcmi: 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>
Acked-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/platform/stm32/stm32-dcmi.c

@@ -1910,10 +1910,13 @@ static int dcmi_probe(struct platform_device *pdev)
 		return PTR_ERR(mclk);
 	}
 
-	chan = dma_request_slave_channel(&pdev->dev, "tx");
-	if (!chan) {
-		dev_info(&pdev->dev, "Unable to request DMA channel, defer probing\n");
-		return -EPROBE_DEFER;
+	chan = dma_request_chan(&pdev->dev, "tx");
+	if (IS_ERR(chan)) {
+		ret = PTR_ERR(chan);
+		if (ret != -EPROBE_DEFER)
+			dev_err(&pdev->dev,
+				"Failed to request DMA channel: %d\n", ret);
+		return ret;
 	}
 
 	spin_lock_init(&dcmi->irqlock);