dm: gpio: Check a GPIO is valid before using it

Since a gpio_desc is allowed to be invalid we should return an error
indicating that the operation cannot be completed. This can happen if the
GPIO is optional - e.g. some devices may have a reset line and some may
not.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/gpio/gpio-uclass.c

@@ -250,8 +250,12 @@ int gpio_free(unsigned gpio)
 
 static int check_reserved(struct gpio_desc *desc, const char *func)
 {
-	struct gpio_dev_priv *uc_priv = dev_get_uclass_priv(desc->dev);
+	struct gpio_dev_priv *uc_priv;
+
+	if (!dm_gpio_is_valid(desc))
+		return -ENOENT;
 
+	uc_priv = dev_get_uclass_priv(desc->dev);
 	if (!uc_priv->name[desc->offset]) {
 		printf("%s: %s: error: gpio %s%d not reserved\n",
 		       desc->dev->name, func,