bus: fsl-mc: MC control registers are not always available

As per the device tree binding, in certain scenarios such as
virtualization scenarios, the MC control registers are not
available so don't error out if they are not present.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Link: https://lore.kernel.org/r/20200914105459.27448-2-laurentiu.tudor@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/bus/fsl-mc/fsl-mc-bus.c

@@ -915,11 +915,11 @@ static int fsl_mc_bus_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, mc);
 
 	plat_res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	mc->fsl_mc_regs = devm_ioremap_resource(&pdev->dev, plat_res);
-	if (IS_ERR(mc->fsl_mc_regs))
-		return PTR_ERR(mc->fsl_mc_regs);
+	if (plat_res)
+		mc->fsl_mc_regs = devm_ioremap_resource(&pdev->dev, plat_res);
 
-	if (IS_ENABLED(CONFIG_ACPI) && !dev_of_node(&pdev->dev)) {
+	if (mc->fsl_mc_regs && IS_ENABLED(CONFIG_ACPI) &&
+	    !dev_of_node(&pdev->dev)) {
 		mc_stream_id = readl(mc->fsl_mc_regs + FSL_MC_FAPR);
 		/*
 		 * HW ORs the PL and BMT bit, places the result in bit 15 of