net: ethernet: cavium: octeon: octeon_mgmt: Handle return NULL error from devm_ioremap

Here, If devm_ioremap will fail. It will return NULL.
Kernel can run into a NULL-pointer dereference.
This error check will avoid NULL pointer dereference.
Signed-off-by: NArvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/octeon/octeon_mgmt.c

@@ -1469,6 +1469,12 @@ static int octeon_mgmt_probe(struct platform_device *pdev)
 	p->agl = (u64)devm_ioremap(&pdev->dev, p->agl_phys, p->agl_size);
 	p->agl_prt_ctl = (u64)devm_ioremap(&pdev->dev, p->agl_prt_ctl_phys,
 					   p->agl_prt_ctl_size);
+	if (!p->mix || !p->agl || !p->agl_prt_ctl) {
+		dev_err(&pdev->dev, "failed to map I/O memory\n");
+		result = -ENOMEM;
+		goto err;
+	}
+
 	spin_lock_init(&p->lock);
 
 	skb_queue_head_init(&p->tx_list);