gpu: ipu-v3: Stop overwriting pdev->dev.of_node of child devices

Setting dev->of_node changes the modalias and breaks module autoloading.
Since there is an of_node field in the platform data passed to child
devices, we don't even need this anymore.

Suggested-by: Russell King <linux@armlinux.org.uk>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>