Add const to parse_{commit,tag}_buffer()

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/tag.c b/tag.c
index f789744..ecf7c1e 100644
--- a/tag.c
+++ b/tag.c
@@ -56,7 +56,7 @@
 	return strtoul(dateptr, NULL, 10);
 }
 
-int parse_tag_buffer(struct tag *item, void *data, unsigned long size)
+int parse_tag_buffer(struct tag *item, const void *data, unsigned long size)
 {
 	unsigned char sha1[20];
 	char type[20];