spi: spi-cadence-quadspi: Fix mapping of buffers for DMA reads

Buffers need to mapped to DMA channel's device pointer instead of SPI
controller's device pointer as its system DMA that actually does data
transfer.
Data inconsistencies have been reported when reading from flash
without this fix.

Fixes: ffa639e ("mtd: spi-nor: cadence-quadspi: Add DMA support for direct mode reads")
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Tested-by: Jan Kiszka <jan.kiszka@siemens.com>
Link: https://lore.kernel.org/r/20200831130720.4524-1-vigneshr@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: r-vignesh

drivers/spi/spi-cadence-quadspi.c

@@ -907,14 +907,16 @@ static int cqspi_direct_read_execute(struct cqspi_flash_pdata *f_pdata,
 	struct dma_async_tx_descriptor *tx;
 	dma_cookie_t cookie;
 	dma_addr_t dma_dst;
+	struct device *ddev;
 
 	if (!cqspi->rx_chan || !virt_addr_valid(buf)) {
 		memcpy_fromio(buf, cqspi->ahb_base + from, len);
 		return 0;
 	}
 
-	dma_dst = dma_map_single(dev, buf, len, DMA_FROM_DEVICE);
-	if (dma_mapping_error(dev, dma_dst)) {
+	ddev = cqspi->rx_chan->device->dev;
+	dma_dst = dma_map_single(ddev, buf, len, DMA_FROM_DEVICE);
+	if (dma_mapping_error(ddev, dma_dst)) {
 		dev_err(dev, "dma mapping failed\n");
 		return -ENOMEM;
 	}
@@ -948,7 +950,7 @@ static int cqspi_direct_read_execute(struct cqspi_flash_pdata *f_pdata,
 	}
 
 err_unmap:
-	dma_unmap_single(dev, dma_dst, len, DMA_FROM_DEVICE);
+	dma_unmap_single(ddev, dma_dst, len, DMA_FROM_DEVICE);
 
 	return ret;
 }