iio:ad7266: Fix broken regulator error handling

All regulator_get() variants return either a pointer to a regulator or an
ERR_PTR() so testing for NULL makes no sense and may lead to bugs if we
use NULL as a valid regulator. Fix this by using IS_ERR() as expected.
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/ad7266.c

@@ -397,7 +397,7 @@ static int ad7266_probe(struct spi_device *spi)
 	st = iio_priv(indio_dev);
 
 	st->reg = devm_regulator_get(&spi->dev, "vref");
-	if (!IS_ERR_OR_NULL(st->reg)) {
+	if (!IS_ERR(st->reg)) {
 		ret = regulator_enable(st->reg);
 		if (ret)
 			return ret;