hrt_ioctl: Fix issue with SMP

The interrupt handler needs to take the spinlock as well, as another
CPU can be futzing around with the lists when another CPU takes the
HRT trap.

platforms/nuttx/src/px4/common/hrt_ioctl.c

@@ -181,13 +181,16 @@ void hrt_usr_call(void *arg)
 {
 	// This is called from hrt interrupt
 	struct usr_hrt_call *e = (struct usr_hrt_call *)arg;
+	irqstate_t flags = spin_lock_irqsave_wo_note(&g_hrt_ioctl_lock);
 
 	// Make sure the event is not already in flight
 	if (!entry_inlist(&callout_inflight, (sq_entry_t *)e)) {
 		sq_rem(&e->list_item, &callout_queue);
 		sq_addfirst(&e->list_item, &callout_inflight);
 		px4_sem_post(e->entry.callout_sem);
 	}
+
+	spin_unlock_irqrestore_wo_note(&g_hrt_ioctl_lock, flags);
 }
 
 int hrt_ioctl(unsigned int cmd, unsigned long arg);