regulator: core: Fix regualtor_ena_gpio_free not to access pin after freeing

After freeing pin from regulator_ena_gpio_free, loop can access
the pin. So this patch fixes not to access pin after freeing.
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -1713,6 +1713,8 @@ static void regulator_ena_gpio_free(struct regulator_dev *rdev)
 				gpiod_put(pin->gpiod);
 				list_del(&pin->list);
 				kfree(pin);
+				rdev->ena_pin = NULL;
+				return;
 			} else {
 				pin->request_count--;
 			}