PCI: Allow PCI express root ports to find themselves

If the pci_find_pcie_root_port() function is called on a root port
itself, return the root port rather than NULL.

This effectively reverts commit 0e405232 ("PCI: fix oops when
try to find Root Port for a PCI device") which added an extra check
that would now be redundant.

Fixes: a99b646a ("PCI: Disable PCIe Relaxed Ordering if unsupported")
Fixes: c56d4450 ("PCI: Turn off Request Attributes to avoid Chelsio T5 Completion erratum")
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Shawn Lin <shawn.lin@rock-chips.com>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/pci/pci.c

@@ -514,7 +514,7 @@ EXPORT_SYMBOL(pci_find_resource);
  */
 struct pci_dev *pci_find_pcie_root_port(struct pci_dev *dev)
 {
-	struct pci_dev *bridge, *highest_pcie_bridge = NULL;
+	struct pci_dev *bridge, *highest_pcie_bridge = dev;
 
 	bridge = pci_upstream_bridge(dev);
 	while (bridge && pci_is_pcie(bridge)) {
@@ -522,11 +522,10 @@ struct pci_dev *pci_find_pcie_root_port(struct pci_dev *dev)
 		bridge = pci_upstream_bridge(bridge);
 	}
 
-	if (highest_pcie_bridge &&
-	    pci_pcie_type(highest_pcie_bridge) == PCI_EXP_TYPE_ROOT_PORT)
-		return highest_pcie_bridge;
-
+	if (pci_pcie_type(highest_pcie_bridge) != PCI_EXP_TYPE_ROOT_PORT)
 		return NULL;
+
+	return highest_pcie_bridge;
 }
 EXPORT_SYMBOL(pci_find_pcie_root_port);