gpiolib: Assign fwnode to parent's if no primary one provided

In case when the properties are supplied in the secondary fwnode
(for example, built-in device properties) the fwnode pointer left
unassigned. This makes unable to retrieve them.

Assign fwnode to parent's if no primary one provided.

Fixes: 7cba1a4 ("gpiolib: generalize devprop_gpiochip_set_names() for device properties")
Fixes: 2afa97e ("gpiolib: Read "gpio-line-names" from a firmware node")
Reported-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Tested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpiolib.c

@@ -571,6 +571,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 			       struct lock_class_key *lock_key,
 			       struct lock_class_key *request_key)
 {
+	struct fwnode_handle *fwnode = gc->parent ? dev_fwnode(gc->parent) : NULL;
 	unsigned long	flags;
 	int		ret = 0;
 	unsigned	i;
@@ -594,6 +595,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 
 	of_gpio_dev_init(gc, gdev);
 
+	/*
+	 * Assign fwnode depending on the result of the previous calls,
+	 * if none of them succeed, assign it to the parent's one.
+	 */
+	gdev->dev.fwnode = dev_fwnode(&gdev->dev) ?: fwnode;
+
 	gdev->id = ida_alloc(&gpio_ida, GFP_KERNEL);
 	if (gdev->id < 0) {
 		ret = gdev->id;