PCI: dwc: Do not remap invalid res

On imx6 and perhaps others when pcie probes you get a:
imx6q-pcie 33800000.pcie: invalid resource

This occurs because the atu is not specified in the DT and as such it
should not be remapped.

Link: https://lore.kernel.org/r/20211101180243.23761-1-tharvey@gateworks.com
Fixes: 281f1f9 ("PCI: dwc: Detect number of iATU windows")
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Richard Zhu <hongxing.zhu@nxp.com>
Cc: Richard Zhu <hongxing.zhu@nxp.com>

Author: Gateworks

drivers/pci/controller/dwc/pcie-designware.c

@@ -672,10 +672,11 @@ void dw_pcie_iatu_detect(struct dw_pcie *pci)
 		if (!pci->atu_base) {
 			struct resource *res =
 				platform_get_resource_byname(pdev, IORESOURCE_MEM, "atu");
-			if (res)
+			if (res) {
 				pci->atu_size = resource_size(res);
-			pci->atu_base = devm_ioremap_resource(dev, res);
-			if (IS_ERR(pci->atu_base))
+				pci->atu_base = devm_ioremap_resource(dev, res);
+			}
+			if (!pci->atu_base || IS_ERR(pci->atu_base))
 				pci->atu_base = pci->dbi_base + DEFAULT_DBI_ATU_OFFSET;
 		}