output drivers: init SmartLock after exit_and_cleanup

This fixes an invalid memory access when exiting the module:
exit_and_cleanup destroys the object, but lock_guard is destructed after
and accesses the lock.

src/drivers/dshot/DShot.cpp

@@ -498,8 +498,6 @@ bool DShot::updateOutputs(bool stop_motors, uint16_t outputs[MAX_ACTUATORS],
 
 void DShot::Run()
 {
-	SmartLock lock_guard(_lock);
-
 	if (should_exit()) {
 		ScheduleClear();
 		_mixing_output.unregister();
@@ -508,6 +506,8 @@ void DShot::Run()
 		return;
 	}
 
+	SmartLock lock_guard(_lock);
+
 	perf_begin(_cycle_perf);
 
 	_mixing_output.update();