regulator: fixed: fix regulator_list_voltage() for regression

Commit c368e5fc2a190923b786f2de3e79430ea3566a25 "regulator: fixed:
get rid of {get|list}_voltage()" broke regulator_list_voltage() for
the fixed regulator, because an earlier commit
5a523605afa7d3b54b2e7041f8c9e6bc39872a7e "regulator: core: provide
fixed voltage in desc for single voltage rail" missed to add support
for the fixed-voltage special case to that function. This patch
fixes that regression.

Signed-off-by: Guennadi Liakhovetski <[email protected]>
Acked-by: Laxman Dewangan <[email protected]>
Signed-off-by: Mark Brown <[email protected]>
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 6382f0a..3fe1313 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2184,6 +2184,9 @@
 	struct regulator_ops	*ops = rdev->desc->ops;
 	int			ret;
 
+	if (rdev->desc->fixed_uV && rdev->desc->n_voltages == 1 && !selector)
+		return rdev->desc->fixed_uV;
+
 	if (!ops->list_voltage || selector >= rdev->desc->n_voltages)
 		return -EINVAL;