Copter: minor change to land mode's logic to use rangefinder

No functional change

ArduCopter/control_land.cpp

@@ -234,7 +234,7 @@ void Copter::land_nogps_run()
 float Copter::get_land_descent_speed()
 {
 #if RANGEFINDER_ENABLED == ENABLED
-    bool rangefinder_ok = rangefinder_state.enabled && (rangefinder.status() == RangeFinder::RangeFinder_Good);
+    bool rangefinder_ok = rangefinder_state.enabled && rangefinder_state.alt_healthy;
 #else
     bool rangefinder_ok = false;
 #endif
@@ -252,7 +252,7 @@ float Copter::get_land_descent_speed()
     }
 
     // if we are above 10m and the rangefinder does not sense anything perform regular alt hold descent
-    if ((target_alt_cm >= LAND_START_ALT) && !(rangefinder_ok && rangefinder_state.alt_healthy)) {
+    if ((target_alt_cm >= LAND_START_ALT) && !rangefinder_ok) {
         if (g.land_speed_high > 0) {
             // user has asked for a different landing speed than normal descent rate
             return -abs(g.land_speed_high);