Reduce excessive FMU stack usage

src/drivers/px4fmu/fmu.cpp

@@ -329,7 +329,7 @@ PX4FMU::init()
 	_task = task_spawn_cmd("fmuservo",
 			       SCHED_DEFAULT,
 			       SCHED_PRIORITY_DEFAULT,
-			       2048,
+			       1600,
 			       (main_t)&PX4FMU::task_main_trampoline,
 			       nullptr);