PCI: keystone: Don't dereference possible NULL pointer

Check for failure from platform_get_resource() (this check actually happens
inside devm_ioremap_resource()) before dereferencing the pointer returned
from platform_get_resource().
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/host/pci-keystone-dw.c

@@ -496,11 +496,12 @@ int __init ks_dw_pcie_host_init(struct keystone_pcie *ks_pcie,
 
 	/* Index 1 is the application reg. space address */
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	ks_pcie->app = *res;
 	ks_pcie->va_app_base = devm_ioremap_resource(pp->dev, res);
 	if (IS_ERR(ks_pcie->va_app_base))
 		return PTR_ERR(ks_pcie->va_app_base);
 
+	ks_pcie->app = *res;
+
 	/* Create legacy IRQ domain */
 	ks_pcie->legacy_irq_domain =
 			irq_domain_add_linear(ks_pcie->legacy_intc_np,