iio: buffer-dmaengine: Use dma_request_chan() directly for channel request

dma_request_slave_channel_reason() is:
	dma_request_chan(dev, name)
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/buffer/industrialio-buffer-dmaengine.c

@@ -150,7 +150,7 @@ struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	if (!dmaengine_buffer)
 		return ERR_PTR(-ENOMEM);
 
-	chan = dma_request_slave_channel_reason(dev, channel);
+	chan = dma_request_chan(dev, channel);
 	if (IS_ERR(chan)) {
 		ret = PTR_ERR(chan);
 		goto err_free;