AP_Scheduler: Use a range of values here because it is valid to do so.

Makes it easier for GUI applications to display this better and valudate the range

libraries/AP_Scheduler/AP_Scheduler.cpp

@@ -61,8 +61,9 @@ const AP_Param::GroupInfo AP_Scheduler::var_info[] = {
     // @Param: LOOP_RATE
     // @DisplayName: Scheduling main loop rate
     // @Description: This controls the rate of the main control loop in Hz. This should only be changed by developers. This only takes effect on restart. Values over 400 are considered highly experimental.
-    // @Values: 50:50Hz,100:100Hz,200:200Hz,250:250Hz,300:300Hz,400:400Hz
+    // @Range: 50 400
     // @RebootRequired: True
+    // @Units: Hz
     // @User: Advanced
     AP_GROUPINFO("LOOP_RATE",  1, AP_Scheduler, _loop_rate_hz, SCHEDULER_DEFAULT_LOOP_RATE),