Revert "mdio_bus: Remove unneeded gpiod NULL check"

This reverts commit 95b80bf3 ("mdio_bus:
Remove unneeded gpiod NULL check"), this commit assumed that GPIOLIB
checks for NULL descriptors, so it's safe to drop them, but it is not
when CONFIG_GPIOLIB is disabled in the kernel. If we do call
gpiod_set_value_cansleep() on a GPIO descriptor we will issue warnings
coming from the inline stubs declared in include/linux/gpio/consumer.h.

Fixes: 95b80bf3 ("mdio_bus: Remove unneeded gpiod NULL check")
Reported-by: Woojung Huh <Woojung.Huh@microchip.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio_bus.c

@@ -399,6 +399,7 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	}
 
 	/* Put PHYs in RESET to save power */
+	if (bus->reset_gpiod)
 		gpiod_set_value_cansleep(bus->reset_gpiod, 1);
 
 	device_del(&bus->dev);
@@ -424,6 +425,7 @@ void mdiobus_unregister(struct mii_bus *bus)
 	}
 
 	/* Put PHYs in RESET to save power */
+	if (bus->reset_gpiod)
 		gpiod_set_value_cansleep(bus->reset_gpiod, 1);
 
 	device_del(&bus->dev);