regulator: core: Change the unit of ramp_delay from mV/uS to uV/uS

This change makes it possible to set ramp_delay with 0.xxx mV/uS without
truncation issue.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/include/linux/regulator/machine.h b/include/linux/regulator/machine.h
index 5f37ad3..40dd0a3 100644
--- a/include/linux/regulator/machine.h
+++ b/include/linux/regulator/machine.h
@@ -92,7 +92,7 @@
  *                 mode.
  * @initial_state: Suspend state to set by default.
  * @initial_mode: Mode to set at startup.
- * @ramp_delay: Time to settle down after voltage change (unit: mV/us)
+ * @ramp_delay: Time to settle down after voltage change (unit: uV/us)
  */
 struct regulation_constraints {