tools lib traceevent: Fix missed freeing of subargs in free_arg() in filter

Some of args were missed in free_args(), as well as subargs.

That is args like FILTER_ARG_NUM have left and right pointers to other
args that also need to be freed.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1349137408.22822.135.camel@gandalf.local.home
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>