PCI: kirin: Return -EPROBE_DEFER in case the gpio isn't ready

PCI host bridge driver can be probed before the gpiochip it requires,
so, of_get_named_gpio() can return -EPROBE_DEFER. Current code lets the
kirin_pcie_probe() directly return -ENODEV, which results in the PCI
host controller driver probe failure; with this error code the PCI host
controller driver will not be probed again when the gpiochip driver is
loaded.

Fix the above issue by letting kirin_pcie_probe() return -EPROBE_DEFER in
such a case.

Link: https://lore.kernel.org/r/20200918123800.19983-1-huobean@gmail.comSigned-off-by: Bean Huo <beanhuo@micron.com>
[lorenzo.pieralisi@arm.com: commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

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

@@ -507,8 +507,12 @@ static int kirin_pcie_probe(struct platform_device *pdev)
 
 	kirin_pcie->gpio_id_reset = of_get_named_gpio(dev->of_node,
 						      "reset-gpios", 0);
-	if (kirin_pcie->gpio_id_reset < 0)
+	if (kirin_pcie->gpio_id_reset == -EPROBE_DEFER) {
+		return -EPROBE_DEFER;
+	} else if (!gpio_is_valid(kirin_pcie->gpio_id_reset)) {
+		dev_err(dev, "unable to get a valid gpio pin\n");
 		return -ENODEV;
+	}
 
 	ret = kirin_pcie_power_on(kirin_pcie);
 	if (ret)