regulator: Appease smatch in regulator_register()

We don't support missing configs at all so segfaulting isn't that bad
but since we've got checks in the code move the dereference after them.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/core.c

@@ -2833,13 +2833,15 @@ regulator_register(const struct regulator_desc *regulator_desc,
 	const struct regulator_init_data *init_data;
 	static atomic_t regulator_no = ATOMIC_INIT(0);
 	struct regulator_dev *rdev;
-	struct device *dev = config->dev;
+	struct device *dev;
 	int ret, i;
 	const char *supply = NULL;
 
 	if (regulator_desc == NULL || config == NULL)
 		return ERR_PTR(-EINVAL);
 
+	dev = config->dev;
+
 	if (regulator_desc->name == NULL || regulator_desc->ops == NULL)
 		return ERR_PTR(-EINVAL);