mmc: mtk-sd: check for valid optional memory resource

'top_base' memory region is optional. Check that the resource is valid
before using it. This avoid getting a "invalid resource" error message
printed by the kernel.
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/mtk-sd.c

@@ -2134,9 +2134,11 @@ static int msdc_drv_probe(struct platform_device *pdev)
 	}
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	host->top_base = devm_ioremap_resource(&pdev->dev, res);
-	if (IS_ERR(host->top_base))
-		host->top_base = NULL;
+	if (res) {
+		host->top_base = devm_ioremap_resource(&pdev->dev, res);
+		if (IS_ERR(host->top_base))
+			host->top_base = NULL;
+	}
 
 	ret = mmc_regulator_get_supply(mmc);
 	if (ret)