regulator: core: Allow fixed enable_time to be set in the regulator_desc

Many regulators have a fixed specification for their enable time. Allow
this to be set in the regulator_desc as a number to save them having to
implement an explicit operation.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index aa82c04..6e488aa 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1189,7 +1189,7 @@
 static int _regulator_get_enable_time(struct regulator_dev *rdev)
 {
 	if (!rdev->desc->ops->enable_time)
-		return 0;
+		return rdev->desc->enable_time;
 	return rdev->desc->ops->enable_time(rdev);
 }