ArduSub: rename OpticalFlow class to AP_OpticalFlow

Brings us in-line with other classes in ArduPilot.

Removes ambiguity with AP_HAL::OpticalFlow which can cause compilation errors as we start to make code more portable across targets

ArduSub/ArduSub.cpp

@@ -72,7 +72,7 @@ const AP_Scheduler::Task Sub::scheduler_tasks[] = {
     SCHED_TASK(fifty_hz_loop,         50,     75,   3),
     SCHED_TASK_CLASS(AP_GPS, &sub.gps, update, 50, 200,   6),
 #if AP_OPTICALFLOW_ENABLED
-    SCHED_TASK_CLASS(OpticalFlow,          &sub.optflow,             update,         200, 160,   9),
+    SCHED_TASK_CLASS(AP_OpticalFlow,          &sub.optflow,             update,         200, 160,   9),
 #endif
     SCHED_TASK(update_batt_compass,   10,    120,  12),
     SCHED_TASK(read_rangefinder,      20,    100,  15),

ArduSub/GCS_Sub.cpp

@@ -57,7 +57,7 @@ void GCS_Sub::update_vehicle_sensor_status_flags()
     }
 
 #if AP_OPTICALFLOW_ENABLED
-    const OpticalFlow *optflow = AP::opticalflow();
+    const AP_OpticalFlow *optflow = AP::opticalflow();
     if (optflow && optflow->enabled()) {
         control_sensors_present |= MAV_SYS_STATUS_SENSOR_OPTICAL_FLOW;
         control_sensors_enabled |= MAV_SYS_STATUS_SENSOR_OPTICAL_FLOW;

ArduSub/Parameters.cpp

@@ -596,7 +596,7 @@ const AP_Param::Info Sub::var_info[] = {
 #if AP_OPTICALFLOW_ENABLED
     // @Group: FLOW
     // @Path: ../libraries/AP_OpticalFlow/AP_OpticalFlow.cpp
-    GOBJECT(optflow,   "FLOW", OpticalFlow),
+    GOBJECT(optflow,   "FLOW", AP_OpticalFlow),
 #endif
 
 #if RPM_ENABLED == ENABLED

ArduSub/Sub.h

@@ -163,7 +163,7 @@ private:
 
     // Optical flow sensor
 #if AP_OPTICALFLOW_ENABLED
-    OpticalFlow optflow;
+    AP_OpticalFlow optflow;
 #endif
 
     // system time in milliseconds of last recorded yaw reset from ekf