spi: at91-usart: Remove some dead code

dma_request_chan() does not return NULL. It returns a valid pointer or an
error pointer.

So, some dead code can be removed.

The IS_ERR_OR_NULL() in the error handling path are still needed, because
the error handling path is common to the whole function and the
ctlr->dma_xx are NULL when at91_usart_spi_configure_dma() is called.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/84eb08daf85d203b34af9d8d08abf86804211413.1694961365.git.christophe.jaillet@wanadoo.frSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-at91-usart.c

@@ -132,28 +132,14 @@ static int at91_usart_spi_configure_dma(struct spi_controller *ctlr,
 	dma_cap_set(DMA_SLAVE, mask);
 
 	ctlr->dma_tx = dma_request_chan(dev, "tx");
-	if (IS_ERR_OR_NULL(ctlr->dma_tx)) {
-		if (IS_ERR(ctlr->dma_tx)) {
-			err = PTR_ERR(ctlr->dma_tx);
-			goto at91_usart_spi_error_clear;
-		}
-
-		dev_dbg(dev,
-			"DMA TX channel not available, SPI unable to use DMA\n");
-		err = -EBUSY;
+	if (IS_ERR(ctlr->dma_tx)) {
+		err = PTR_ERR(ctlr->dma_tx);
 		goto at91_usart_spi_error_clear;
 	}
 
 	ctlr->dma_rx = dma_request_chan(dev, "rx");
-	if (IS_ERR_OR_NULL(ctlr->dma_rx)) {
-		if (IS_ERR(ctlr->dma_rx)) {
-			err = PTR_ERR(ctlr->dma_rx);
-			goto at91_usart_spi_error;
-		}
-
-		dev_dbg(dev,
-			"DMA RX channel not available, SPI unable to use DMA\n");
-		err = -EBUSY;
+	if (IS_ERR(ctlr->dma_rx)) {
+		err = PTR_ERR(ctlr->dma_rx);
 		goto at91_usart_spi_error;
 	}