regulators: Remove monitoring freq from comments

Update doxygen comments to remove the exact frequency of sensor
monitoring and phase fault detection.

Currently sensors are monitored every second and phase faults are
detected every 15 seconds.  However, that could change in the future.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I3ac39955721fde98dfe9e6059693ceeea7e504c2
diff --git a/phosphor-regulators/src/rail.hpp b/phosphor-regulators/src/rail.hpp
index 5591c36..63d80eb 100644
--- a/phosphor-regulators/src/rail.hpp
+++ b/phosphor-regulators/src/rail.hpp
@@ -119,7 +119,7 @@
      * Sensor monitoring is optional.  If sensor monitoring is defined for this
      * rail, the sensor values are read.
      *
-     * This method should be called once per second.
+     * This method should be called repeatedly based on a timer.
      *
      * @param services system services like error logging and the journal
      * @param system system that contains the chassis