AP_Avoidance: tidy construction of vector on stack

libraries/AP_Avoidance/AP_Avoidance.cpp

@@ -599,9 +599,11 @@ void AP_Avoidance::handle_msg(const mavlink_message_t &msg)
         int32_t(packet.alt * 0.1),  // mm -> cm
         Location::AltFrame::ABSOLUTE
     };
-    Vector3f vel = Vector3f(packet.vx/100.0f, // cm to m
-                            packet.vy/100.0f,
-                            packet.vz/100.0f);
+    const Vector3f vel {
+        packet.vx * 0.01f, // cm to m
+        packet.vy * 0.01f,
+        packet.vz * 0.01f
+    };
     add_obstacle(AP_HAL::millis(),
                  MAV_COLLISION_SRC_MAVLINK_GPS_GLOBAL_INT,
                  msg.sysid,