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/pwm_out_sim/PWMSim.cpp

@@ -58,8 +58,6 @@ PWMSim::PWMSim(bool hil_mode_enabled) :
 void
 PWMSim::Run()
 {
-	SmartLock lock_guard(_lock);
-
 	if (should_exit()) {
 		ScheduleClear();
 		_mixing_output.unregister();
@@ -68,6 +66,8 @@ PWMSim::Run()
 		return;
 	}
 
+	SmartLock lock_guard(_lock);
+
 	_mixing_output.update();
 
 	// check for parameter updates