perf event parser: Add const qualifier to evt_name and sys_name

Add missing 'const' qualifiers so following commits are able to create
tracepoints using const strings.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1468406646-21642-4-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/parse-events.h b/tools/perf/util/parse-events.h
index 46c05cc..0bd664d 100644
--- a/tools/perf/util/parse-events.h
+++ b/tools/perf/util/parse-events.h
@@ -134,7 +134,7 @@
 int parse_events__modifier_group(struct list_head *list, char *event_mod);
 int parse_events_name(struct list_head *list, char *name);
 int parse_events_add_tracepoint(struct list_head *list, int *idx,
-				char *sys, char *event,
+				const char *sys, const char *event,
 				struct parse_events_error *error,
 				struct list_head *head_config);
 int parse_events_load_bpf(struct parse_events_evlist *data,