regulator: Check ramp_delay_table for regulator_set_ramp_delay_regmap

Return -EINVAL if ramp_delay_table is NULL.
Also add WARN_ON since the driver code needs fix if this happened.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20210519132255.1683863-1-axel.lin@ingics.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/helpers.c

@@ -948,7 +948,7 @@ int regulator_set_ramp_delay_regmap(struct regulator_dev *rdev, int ramp_delay)
 	int ret;
 	unsigned int sel;
 
-	if (!rdev->desc->n_ramp_values)
+	if (WARN_ON(!rdev->desc->n_ramp_values || !rdev->desc->ramp_delay_table))
 		return -EINVAL;
 
 	ret = find_closest_bigger(ramp_delay, rdev->desc->ramp_delay_table,