perf kmem: Fix a memory leak

The 'str' should be freed when sort_dimension__add() failed too.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1325957132-10600-5-git-send-email-namhyung@gmail.com
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-kmem.c

@@ -647,6 +647,7 @@ static int setup_sorting(struct list_head *sort_list, const char *arg)
 			break;
 		if (sort_dimension__add(tok, sort_list) < 0) {
 			error("Unknown --sort key: '%s'", tok);
+			free(str);
 			return -1;
 		}
 	}