mtd: rawnand: cadence: fix unchecked dereference

Add NULL check before variable dereference to fix static checker warning.

Fixes: d76d22b ("mtd: rawnand: cadence: use dma_map_resource for sdma address")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/e448a22c-bada-448d-9167-7af71305130d@stanley.mountain/
Signed-off-by: Niravkumar L Rabara <niravkumar.l.rabara@intel.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: rabara

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

@@ -2972,8 +2972,10 @@ static int cadence_nand_init(struct cdns_nand_ctrl *cdns_ctrl)
 static void cadence_nand_remove(struct cdns_nand_ctrl *cdns_ctrl)
 {
 	cadence_nand_chips_cleanup(cdns_ctrl);
-	dma_unmap_resource(cdns_ctrl->dmac->device->dev, cdns_ctrl->io.iova_dma,
-			   cdns_ctrl->io.size, DMA_BIDIRECTIONAL, 0);
+	if (cdns_ctrl->dmac)
+		dma_unmap_resource(cdns_ctrl->dmac->device->dev,
+				   cdns_ctrl->io.iova_dma, cdns_ctrl->io.size,
+				   DMA_BIDIRECTIONAL, 0);
 	cadence_nand_irq_cleanup(cdns_ctrl->irq, cdns_ctrl);
 	kfree(cdns_ctrl->buf);
 	dma_free_coherent(cdns_ctrl->dev, sizeof(struct cadence_nand_cdma_desc),