regulator: bd9571mwv: fix OF node reference imbalance

The driver reuses the OF node of the parent multi-function device but
fails to take another reference to balance the one dropped by the
platform bus code when unbinding the MFD and deregistering the child
devices.

Fix this by using the intended helper for reusing OF nodes.

Fixes: e85c5a1 ("regulator: Add ROHM BD9571MWV-M PMIC regulator driver")
Cc: stable@vger.kernel.org	# 4.12
Cc: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260408073055.5183-8-johan@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: jhovold

drivers/regulator/bd9571mwv-regulator.c

@@ -287,8 +287,9 @@ static int bd9571mwv_regulator_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, bdreg);
 
+	device_set_of_node_from_dev(&pdev->dev, pdev->dev.parent);
+
 	config.dev = &pdev->dev;
-	config.dev->of_node = pdev->dev.parent->of_node;
 	config.driver_data = bdreg;
 	config.regmap = bdreg->regmap;