spi: atmel: Downgrade to dev_dbg when dma_request_chan() fails

The IP's DMA capabilities are described in the SoC dtsi, to spare
users duplicating the DMA bindings in their board device tree. Users
that don't want to use DMA, have to overwrite the DMA bindings in
their board device tree. An example is:
commit ddcdaeb8 ("ARM: dts: at91: sama5d2: Add DMA bindings for the SPI and UART flx4 functions")

When the DMA bindings are overwritten, one could see on the console:
atmel_spi fc018400.spi: error -ENODEV: No TX DMA channel, DMA is disabled
atmel_spi fc018400.spi: Atmel SPI Controller using PIO only

Choosing to not use DMA is not a reason to print an error message.
More, the user is already informed when PIO is used: "Atmel SPI Controller
using PIO only". Downgrade to dev_dbg when dma_request_chan() fails.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20201030121116.869105-1-tudor.ambarus@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-atmel.c

@@ -512,8 +512,8 @@ static int atmel_spi_configure_dma(struct spi_master *master,
 
 	master->dma_tx = dma_request_chan(dev, "tx");
 	if (IS_ERR(master->dma_tx)) {
-		err = dev_err_probe(dev, PTR_ERR(master->dma_tx),
-				    "No TX DMA channel, DMA is disabled\n");
+		err = PTR_ERR(master->dma_tx);
+		dev_dbg(dev, "No TX DMA channel, DMA is disabled\n");
 		goto error_clear;
 	}
 
@@ -524,7 +524,7 @@ static int atmel_spi_configure_dma(struct spi_master *master,
 		 * No reason to check EPROBE_DEFER here since we have already
 		 * requested tx channel.
 		 */
-		dev_err(dev, "No RX DMA channel, DMA is disabled\n");
+		dev_dbg(dev, "No RX DMA channel, DMA is disabled\n");
 		goto error;
 	}