regulator: axp20x: check rdev is null before dereferencing it

Currently rdev is dereferenced when assigning desc before rdev is null
checked, hence there is a potential null pointer dereference on rdev.
Fix this by null checking rdev first.

Detected by CoverityScan, CID#1476031 ("Dereference before null check")

Fixes: 77e3e3b1 ("regulator: axp20x: add software based soft_start for AXP209 LDO3")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/axp20x-regulator.c

@@ -367,7 +367,7 @@ static const int axp209_dcdc2_ldo3_slew_rates[] = {
 static int axp20x_set_ramp_delay(struct regulator_dev *rdev, int ramp)
 {
 	struct axp20x_dev *axp20x = rdev_get_drvdata(rdev);
-	const struct regulator_desc *desc = rdev->desc;
+	const struct regulator_desc *desc;
 	u8 reg, mask, enable, cfg = 0xff;
 	const int *slew_rates;
 	int rate_count = 0;
@@ -375,6 +375,8 @@ static int axp20x_set_ramp_delay(struct regulator_dev *rdev, int ramp)
 	if (!rdev)
 		return -EINVAL;
 
+	desc = rdev->desc;
+
 	switch (axp20x->variant) {
 	case AXP209_ID:
 		if (desc->id == AXP20X_DCDC2) {
@@ -436,11 +438,13 @@ static int axp20x_set_ramp_delay(struct regulator_dev *rdev, int ramp)
 static int axp20x_regulator_enable_regmap(struct regulator_dev *rdev)
 {
 	struct axp20x_dev *axp20x = rdev_get_drvdata(rdev);
-	const struct regulator_desc *desc = rdev->desc;
+	const struct regulator_desc *desc;
 
 	if (!rdev)
 		return -EINVAL;
 
+	desc = rdev->desc;
+
 	switch (axp20x->variant) {
 	case AXP209_ID:
 		if ((desc->id == AXP20X_LDO3) &&