regulator: scmi: Allow for zero voltage domains

SCMI Voltage protocol allows the platform to report no voltage domains
on discovery, while warning the user about such an odd configuration.
As a consequence this condition should not be treated as error by the SCMI
regulator driver either.

Allow SCMI regulator driver to probe successfully even when no voltage
domains are discovered.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20230126180511.766373-1-cristian.marussi@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/scmi-regulator.c

@@ -311,16 +311,12 @@ static int scmi_regulator_probe(struct scmi_device *sdev)
 		return PTR_ERR(voltage_ops);
 
 	num_doms = voltage_ops->num_domains_get(ph);
-	if (num_doms <= 0) {
-		if (!num_doms) {
-			dev_err(&sdev->dev,
-				"number of voltage domains invalid\n");
-			num_doms = -EINVAL;
-		} else {
-			dev_err(&sdev->dev,
-				"failed to get voltage domains - err:%d\n",
-				num_doms);
-		}
+	if (!num_doms)
+		return 0;
+
+	if (num_doms < 0) {
+		dev_err(&sdev->dev, "failed to get voltage domains - err:%d\n",
+			num_doms);
 
 		return num_doms;
 	}