usb: phy: make GPIOs optional for the generic phy

The use of GPIOs should be optional for the generic phy, otherwise
the Altera SOCFPGA platform at least is broken.

Fixes breakage caused by a combination of e9f2cefb0cd "usb: phy:
generic: migrate to gpio_desc" and 135b3c4304d "usb: dwc2: platform:
add generic PHY framework support".

Reviewed-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/phy/phy-generic.c

@@ -218,10 +218,10 @@ int usb_phy_gen_create_phy(struct device *dev, struct usb_phy_generic *nop,
 			clk_rate = 0;
 
 		needs_vcc = of_property_read_bool(node, "vcc-supply");
-		nop->gpiod_reset = devm_gpiod_get(dev, "reset-gpios");
+		nop->gpiod_reset = devm_gpiod_get_optional(dev, "reset-gpios");
 		err = PTR_ERR(nop->gpiod_reset);
 		if (!err) {
-			nop->gpiod_vbus = devm_gpiod_get(dev,
+			nop->gpiod_vbus = devm_gpiod_get_optional(dev,
 							 "vbus-detect-gpio");
 			err = PTR_ERR(nop->gpiod_vbus);
 		}