cpu/native: fix memory leak
cpu/native: fix memory leak

In make_message API in syscall.c, memory should be freed before returning
Fixes issue: #15016

Signed-off-by: avinash <000c5fdbcd0e065492d0cd60f166ae2d4f75649b@gmail.com>

authmillenon/RIOT,kYc0o/RIOT,miri64/RIOT,jasonatran/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,ant9000/RIOT,ant9000/RIOT,authmillenon/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,ant9000/RIOT,OTAkeys/RIOT,authmillenon/RIOT,miri64/RIOT,OlegHahm/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kYc0o/RIOT,kaspar030/RIOT,kYc0o/RIOT,OTAkeys/RIOT,authmillenon/RIOT,ant9000/RIOT,miri64/RIOT,jasonatran/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kaspar030/RIOT,OTAkeys/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,miri64/RIOT,OTAkeys/RIOT,kaspar030/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,jasonatran/RIOT