regulator: gpio: check return value of of_get_named_gpio

At boot time the regulator driver can be initialized before the
gpio, in which case the call to of_get_named_gpio will return
EPROBE_DEFER. This value is silently passed to regulator_register
which will return success, although the gpio is not registered
(regulator_ena_gpio_request not called) as the value passed is
detected as invalid. The gpio_regulator_probe will therefore
succeed win no gpio requested.
Signed-off-by: Mihai Mihalache <mihai.d.mihalache@intel.com>
Reviewed-by: Hans Holmberg <hans.holmberg@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/gpio-regulator.c

@@ -162,6 +162,8 @@ of_get_gpio_regulator_config(struct device *dev, struct device_node *np,
 	of_property_read_u32(np, "startup-delay-us", &config->startup_delay);
 
 	config->enable_gpio = of_get_named_gpio(np, "enable-gpio", 0);
+	if (config->enable_gpio == -EPROBE_DEFER)
+		return ERR_PTR(-EPROBE_DEFER);
 
 	/* Fetch GPIOs. - optional property*/
 	ret = of_gpio_count(np);