iio: devm_regulator_get_optional never returns NULL

This patch is inspired by a comment of Jonathan Cameron on patch of
Linus Walleij commit aeb55fff3891834e07a3144159a7298a19696af8 ("iio:
st_sensors: fetch and enable regulators unconditionally"). Because
changes made in this patch are actually reference generators they should
be using devm_regulator_get_optional, but if they do not explicitly set
the reference to NULL they should not be using IS_ERR_OR_NULL, but
simple IS_ERR check.

Suggested-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Crt Mori <cmo@melexis.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/ad7266.c

@@ -481,7 +481,7 @@ error_free_gpios:
 	if (!st->fixed_addr)
 		gpio_free_array(st->gpios, ARRAY_SIZE(st->gpios));
 error_disable_reg:
-	if (!IS_ERR_OR_NULL(st->reg))
+	if (!IS_ERR(st->reg))
 		regulator_disable(st->reg);
 
 	return ret;
@@ -496,7 +496,7 @@ static int ad7266_remove(struct spi_device *spi)
 	iio_triggered_buffer_cleanup(indio_dev);
 	if (!st->fixed_addr)
 		gpio_free_array(st->gpios, ARRAY_SIZE(st->gpios));
-	if (!IS_ERR_OR_NULL(st->reg))
+	if (!IS_ERR(st->reg))
 		regulator_disable(st->reg);
 
 	return 0;

drivers/iio/adc/ti-ads8688.c

@@ -438,7 +438,7 @@ static int ads8688_probe(struct spi_device *spi)
 	return 0;
 
 error_out:
-	if (!IS_ERR_OR_NULL(st->reg))
+	if (!IS_ERR(st->reg))
 		regulator_disable(st->reg);
 
 	return ret;
@@ -451,7 +451,7 @@ static int ads8688_remove(struct spi_device *spi)
 
 	iio_device_unregister(indio_dev);
 
-	if (!IS_ERR_OR_NULL(st->reg))
+	if (!IS_ERR(st->reg))
 		regulator_disable(st->reg);
 
 	return 0;