ptz: Fix wrongly sending recall command continuously

Using "VISCA over TCP" and the recall is enabled, the recall command was
continuously sent once a recall is requested.

src/libvisca-thread.cpp

@@ -155,7 +155,7 @@ void libvisca_thread::thread_loop()
 			ptz_changed = true;
 		}
 
-		if (os_atomic_load_bool(&preset_changed)) {
+		if (os_atomic_set_bool(&preset_changed, false)) {
 			os_sleep_ms(48);
 			VISCA_memory_recall(iface, camera, preset_rsvd);
 			os_sleep_ms(48);