tools lib traceevent: Free filter tokens in process_filter()

valgrind showed that the filter token wasn't being freed properly in
process_filter().

Signed-off-by: Steven Rostedt <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/traceevent/parse-filter.c

···
 					*parg = current_op;
 				else
 					*parg = current_exp;
+				free(token);
 				return PEVENT_ERRNO__UNBALANCED_PAREN;
 			}
 			break;
···
 
 	*parg = current_op;
 
+	free(token);
 	return 0;
 
  fail_alloc: