AP_Scheduler: add floating point specifier on constant

libraries/AP_Scheduler/AP_Scheduler.h

@@ -126,7 +126,7 @@ public:
     // get the time-allowed-per-loop in seconds
     float get_loop_period_s() {
         if (is_zero(_loop_period_s)) {
-            _loop_period_s = 1.0 / _loop_rate_hz;
+            _loop_period_s = 1.0f / _loop_rate_hz;
         }
         return _loop_period_s;
     }