iio: dac: ad5592r: Get rid of OF specifics

Use dev_fwnode() instead of direct OF node dereference when checking
for regulator API error code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220531135320.63096-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad5592r-base.c

@@ -603,7 +603,7 @@ int ad5592r_probe(struct device *dev, const char *name,
 
 	st->reg = devm_regulator_get_optional(dev, "vref");
 	if (IS_ERR(st->reg)) {
-		if ((PTR_ERR(st->reg) != -ENODEV) && dev->of_node)
+		if ((PTR_ERR(st->reg) != -ENODEV) && dev_fwnode(dev))
 			return PTR_ERR(st->reg);
 
 		st->reg = NULL;