pci: Flip condition for detecting non-PCI parent devices

pci: Flip condition for detecting non-PCI parent devices

In pci_uclass_pre_probe an attempt is made to detect whether the parent
of a device is a PCI device and that the device is thus a bridge. This
was being done by checking whether the parent of the device is of the
UCLASS_ROOT class. This causes problems if the PCI controller is a child
of some other non-PCI node, for example a simple-bus node.

For example, if the device tree contains something like the following
then pci_uclass_pre_probe would incorrectly believe that the PCI
controller is a bridge, with a PCI parent:

  / {
    some_child {
      compatible = "simple-bus";
      #address-cells = <1>;
      #size-cells = <1>;
      ranges = <>;

      pci_controller: pci@10000000 {
        compatible = "my-pci-controller";
        device_type = "pci";
        reg = <0x10000000 0x2000000>;
      };
    };
  };

Avoid this incorrect detection of bridges by instead checking whether
the parent devices class is UCLASS_PCI and treating a device as a bridge
when this is true, making use of device_is_on_pci_bus to perform this
test.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Simon Glass <sjg@chromium.org>