regulator: da9063: fix null pointer deref with partial DT config

When some of the da9063 regulators do not have corresponding DT nodes
a null pointer dereference occurs on boot because such regulators have
no init_data causing the pointers calculated in
da9063_check_xvp_constraints() to be invalid.

Do not dereference them in this case.

Fixes: b8717a80 ("regulator: da9063: implement setter for voltage monitoring")
Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
Link: https://lore.kernel.org/r/20230616143736.2946173-1-martin.fuzzey@flowbird.groupSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/da9063-regulator.c

@@ -778,6 +778,9 @@ static int da9063_check_xvp_constraints(struct regulator_config *config)
 	const struct notification_limit *uv_l = &constr->under_voltage_limits;
 	const struct notification_limit *ov_l = &constr->over_voltage_limits;
 
+	if (!config->init_data) /* No config in DT, pointers will be invalid */
+		return 0;
+
 	/* make sure that only one severity is used to clarify if unchanged, enabled or disabled */
 	if ((!!uv_l->prot + !!uv_l->err + !!uv_l->warn) > 1) {
 		dev_err(config->dev, "%s: at most one voltage monitoring severity allowed!\n",