AP_HAL_PX4: compiler warnings: float to doubles

libraries/AP_HAL_PX4/Util.cpp

@@ -93,7 +93,7 @@ enum PX4Util::safety_state PX4Util::safety_switch_state(void)
 void PX4Util::set_system_clock(uint64_t time_utc_usec)
 {
     timespec ts;
-    ts.tv_sec = time_utc_usec/1.0e6;
+    ts.tv_sec = time_utc_usec/1.0e6f;
     ts.tv_nsec = (time_utc_usec % 1000000) * 1000;
     clock_settime(CLOCK_REALTIME, &ts);    
 }