CVE-2022-49800 tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth_event()

In the Linux kernel, the following vulnerability has been resolved: tracing: Fix memory leak in testgensynthcmd and testemptysynthevent testgensynthcmd only free buf in fail path, hence buf will leak when there is no failure. Add kfreebuf to prevent the memleak. The same reason and solution in...