Rover: gyro health check uses initialised flag

We should not be relying on the notify flags as a way to pass info around the system.  Rover's initialised flag is equivalent and more appropriate.

APMrover2/sensors.cpp

@@ -362,7 +362,7 @@ void Rover::update_sensor_status_flags(void)
         control_sensors_health &= ~MAV_SYS_STATUS_LOGGING;
     }
 
-    if (AP_Notify::flags.initialising) {
+    if (!initialised || ins.calibrating()) {
         // while initialising the gyros and accels are not enabled
         control_sensors_enabled &= ~(MAV_SYS_STATUS_SENSOR_3D_GYRO | MAV_SYS_STATUS_SENSOR_3D_ACCEL);
         control_sensors_health &= ~(MAV_SYS_STATUS_SENSOR_3D_GYRO | MAV_SYS_STATUS_SENSOR_3D_ACCEL);