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/commit.c b/commit.c
index 74d6601..ac337c7 100644
--- a/commit.c
+++ b/commit.c
@@ -245,10 +245,10 @@
 	return 0;
 }
 
-int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
+int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size)
 {
-	char *tail = buffer;
-	char *bufptr = buffer;
+	const char *tail = buffer;
+	const char *bufptr = buffer;
 	unsigned char parent[20];
 	struct commit_list **pptr;
 	struct commit_graft *graft;