gpio: fix NULL-deref-on-deregistration regression

Fix a NULL-pointer deference when deregistering the gpio character
device that was introduced by the recent stub-driver hack. When the new
"driver" is unbound as part of deregistration, driver core clears the
driver-data pointer which is used to retrieve the struct gpio_device in
its release callback.

Fix this by using container_of() in the release callback as should have
been done all along.

Fixes: 4731210c ("gpiolib: Bind gpio_device to a driver to enable fw_devlink=on by default")
Cc: Saravana Kannan <saravanak@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reported-by: syzbot+d27b4c8adbbff70fbfde@syzkaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpiolib.c

@@ -474,7 +474,7 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
 
 static void gpiodevice_release(struct device *dev)
 {
-	struct gpio_device *gdev = dev_get_drvdata(dev);
+	struct gpio_device *gdev = container_of(dev, struct gpio_device, dev);
 
 	list_del(&gdev->list);
 	ida_free(&gpio_ida, gdev->id);
@@ -605,7 +605,6 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		goto err_free_ida;
 
 	device_initialize(&gdev->dev);
-	dev_set_drvdata(&gdev->dev, gdev);
 	if (gc->parent && gc->parent->driver)
 		gdev->owner = gc->parent->driver->owner;
 	else if (gc->owner)