cmake topic_listener: make topic_listener.cpp depend on msg_gen

This makes sure the .cpp file is regenerated on .msg file changes

src/systemcmds/topic_listener/CMakeLists.txt

@@ -33,6 +33,7 @@
 
 add_custom_command(OUTPUT topic_listener.cpp
                 COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_SOURCE_DIR}/Tools/generate_listener.py ${CMAKE_SOURCE_DIR} > topic_listener.cpp
+                DEPENDS msg_gen
                 )
 
 add_custom_target(generate_topic_listener
@@ -51,6 +52,5 @@ px4_add_module(
 	DEPENDS
 		platforms__common
 		generate_topic_listener
-		msg_gen
 	)
 # vim: set noet ft=cmake fenc=utf-8 ff=unix :