mtd: rawnand: cadence: fix DMA device NULL pointer dereference

The DMA device pointer `dma_dev` was being dereferenced before ensuring
that `cdns_ctrl->dmac` is properly initialized.

Move the assignment of `dma_dev` after successfully acquiring the DMA
channel to ensure the pointer is valid before use.

Fixes: d76d22b ("mtd: rawnand: cadence: use dma_map_resource for sdma address")
Cc: [email protected]
Signed-off-by: Niravkumar L Rabara <[email protected]>
Signed-off-by: Miquel Raynal <[email protected]>

Author: rabara

drivers/mtd/nand/raw/cadence-nand-controller.c

@@ -2871,7 +2871,7 @@ cadence_nand_irq_cleanup(int irqnum, struct cdns_nand_ctrl *cdns_ctrl)
 static int cadence_nand_init(struct cdns_nand_ctrl *cdns_ctrl)
 {
 	dma_cap_mask_t mask;
-	struct dma_device *dma_dev = cdns_ctrl->dmac->device;
+	struct dma_device *dma_dev;
 	int ret;
 
 	cdns_ctrl->cdma_desc = dma_alloc_coherent(cdns_ctrl->dev,
@@ -2915,6 +2915,7 @@ static int cadence_nand_init(struct cdns_nand_ctrl *cdns_ctrl)
 		}
 	}
 
+	dma_dev = cdns_ctrl->dmac->device;
 	cdns_ctrl->io.iova_dma = dma_map_resource(dma_dev->dev, cdns_ctrl->io.dma,
 						  cdns_ctrl->io.size,
 						  DMA_BIDIRECTIONAL, 0);