PCI: xgene: Fix cfg resource mapping

In commit e2dcd20 a change was made to use
devm_platform_ioremap_resource_byname() to simplify code and remove
the res variable; this was wrong since the res variable is still needed
and as an outcome the port->cfg_addr gets an erroneous address.

Revert the change going back to original behaviour.

Link: https://lore.kernel.org/r/20210328144118.305074-1-zhengdejin5@gmail.com
Fixes: e2dcd20 ("PCI: controller: Convert to devm_platform_ioremap_resource_byname()")
Reported-by: dann.frazier@canonical.com
Tested-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org    # v5.9+

Author: Dejin Zheng

drivers/pci/controller/pci-xgene.c

@@ -354,7 +354,8 @@ static int xgene_pcie_map_reg(struct xgene_pcie_port *port,
 	if (IS_ERR(port->csr_base))
 		return PTR_ERR(port->csr_base);
 
-	port->cfg_base = devm_platform_ioremap_resource_byname(pdev, "cfg");
+	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "cfg");
+	port->cfg_base = devm_ioremap_resource(dev, res);
 	if (IS_ERR(port->cfg_base))
 		return PTR_ERR(port->cfg_base);
 	port->cfg_addr = res->start;