PCI: rockchip: Make 'ep-gpios' DT property optional

The Rockchip PCIe controller DT binding clearly states that 'ep-gpios' is
an optional property. And indeed there are boards that don't require it.

Make the driver follow the binding by using devm_gpiod_get_optional()
instead of devm_gpiod_get().

[bhelgaas: tidy whitespace]
Link: https://lore.kernel.org/r/20210121162321.4538-2-wens@kernel.org
Fixes: e77f847d ("PCI: rockchip: Add Rockchip PCIe controller support")
Fixes: 956cd99b ("PCI: rockchip: Separate common code from RC driver")
Fixes: 964bac94 ("PCI: rockchip: Split out rockchip_pcie_parse_dt() to parse DT")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/controller/pcie-rockchip.c

@@ -118,11 +118,11 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
 	}
 
 	if (rockchip->is_rc) {
-		rockchip->ep_gpio = devm_gpiod_get(dev, "ep", GPIOD_OUT_HIGH);
-		if (IS_ERR(rockchip->ep_gpio)) {
-			dev_err(dev, "missing ep-gpios property in node\n");
-			return PTR_ERR(rockchip->ep_gpio);
-		}
+		rockchip->ep_gpio = devm_gpiod_get_optional(dev, "ep",
+							    GPIOD_OUT_HIGH);
+		if (IS_ERR(rockchip->ep_gpio))
+			return dev_err_probe(dev, PTR_ERR(rockchip->ep_gpio),
+					     "failed to get ep GPIO\n");
 	}
 
 	rockchip->aclk_pcie = devm_clk_get(dev, "aclk");