spi: fsl-dspi: Preserve error code returned by dmaengine_slave_config()

dmaengine_slave_config() may return different error codes based on
the circumstances. Preserve it instead of shadowing to -EINVAL.
Suggested-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20240204203127.1186621-2-andy.shevchenko@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -542,7 +542,6 @@ static int dspi_request_dma(struct fsl_dspi *dspi, phys_addr_t phy_addr)
 	ret = dmaengine_slave_config(dma->chan_rx, &cfg);
 	if (ret) {
 		dev_err(dev, "can't configure rx dma channel\n");
-		ret = -EINVAL;
 		goto err_slave_config;
 	}
 
@@ -550,7 +549,6 @@ static int dspi_request_dma(struct fsl_dspi *dspi, phys_addr_t phy_addr)
 	ret = dmaengine_slave_config(dma->chan_tx, &cfg);
 	if (ret) {
 		dev_err(dev, "can't configure tx dma channel\n");
-		ret = -EINVAL;
 		goto err_slave_config;
 	}