mailbox: xgene-slimpro: Fix potential NULL pointer dereference

There is a potential execution path in which function
platform_get_resource() returns NULL. If this happens,
we will end up having a NULL pointer dereference.

Fix this by replacing devm_ioremap with devm_ioremap_resource,
which has the NULL check and the memory region request.

This code was detected with the help of Coccinelle.

Cc: stable@vger.kernel.org
Fixes: f700e84f417b ("mailbox: Add support for APM X-Gene platform mailbox driver")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/mailbox-xgene-slimpro.c

@@ -195,9 +195,9 @@ static int slimpro_mbox_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, ctx);
 
 	regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	mb_base = devm_ioremap(&pdev->dev, regs->start, resource_size(regs));
-	if (!mb_base)
-		return -ENOMEM;
+	mb_base = devm_ioremap_resource(&pdev->dev, regs);
+	if (IS_ERR(mb_base))
+		return PTR_ERR(mb_base);
 
 	/* Setup mailbox links */
 	for (i = 0; i < MBOX_CNT; i++) {