regulator: core: request only valid gpio pins for regulator enable

Commit 65f7350 ("regulator: core: Add core support for GPIO controlled
enable lines") introduced enable gpio entry in regulator configuration
structure. Some drivers use '-1' as a placeholder for marking that such
gpio line is not available, because '0' is considered as a valid gpio
number. This patch fixes initialization of such drivers (like MAX8952
on UniversalC210 board), when '-1' is provided as enable gpio pin in the
regulator's platform data.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/core.c

@@ -3217,7 +3217,7 @@ regulator_register(const struct regulator_desc *regulator_desc,
 
 	dev_set_drvdata(&rdev->dev, rdev);
 
-	if (config->ena_gpio) {
+	if (config->ena_gpio && gpio_is_valid(config->ena_gpio)) {
 		ret = gpio_request_one(config->ena_gpio,
 				       GPIOF_DIR_OUT | config->ena_gpio_flags,
 				       rdev_get_name(rdev));