media: xilinx: 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 <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/xilinx/xilinx-dma.c

···
 
 	/* ... and the DMA channel. */
 	snprintf(name, sizeof(name), "port%u", port);
-	dma->dma = dma_request_slave_channel(dma->xdev->dev, name);
-	if (dma->dma == NULL) {
-		dev_err(dma->xdev->dev, "no VDMA channel found\n");
-		ret = -ENODEV;
+	dma->dma = dma_request_chan(dma->xdev->dev, name);
+	if (IS_ERR(dma->dma)) {
+		ret = PTR_ERR(dma->dma);
+		if (ret != -EPROBE_DEFER)
+			dev_err(dma->xdev->dev, "no VDMA channel found\n");
 		goto error;
 	}
 
···
 	if (video_is_registered(&dma->video))
 		video_unregister_device(&dma->video);
 
-	if (dma->dma)
+	if (!IS_ERR_OR_NULL(dma->dma))
 		dma_release_channel(dma->dma);
 
 	media_entity_cleanup(&dma->video.entity);