spi: img-spfi: 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/20191212135550.4634-5-peter.ujfalusi@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-img-spfi.c

@@ -666,8 +666,22 @@ static int img_spfi_probe(struct platform_device *pdev)
 	master->unprepare_message = img_spfi_unprepare;
 	master->handle_err = img_spfi_handle_err;
 
-	spfi->tx_ch = dma_request_slave_channel(spfi->dev, "tx");
-	spfi->rx_ch = dma_request_slave_channel(spfi->dev, "rx");
+	spfi->tx_ch = dma_request_chan(spfi->dev, "tx");
+	if (IS_ERR(spfi->tx_ch)) {
+		ret = PTR_ERR(spfi->tx_ch);
+		spfi->tx_ch = NULL;
+		if (ret == -EPROBE_DEFER)
+			goto disable_pm;
+	}
+
+	spfi->rx_ch = dma_request_chan(spfi->dev, "rx");
+	if (IS_ERR(spfi->rx_ch)) {
+		ret = PTR_ERR(spfi->rx_ch);
+		spfi->rx_ch = NULL;
+		if (ret == -EPROBE_DEFER)
+			goto disable_pm;
+	}
+
 	if (!spfi->tx_ch || !spfi->rx_ch) {
 		if (spfi->tx_ch)
 			dma_release_channel(spfi->tx_ch);