Fix typo in comments of longest_ancestor_length()

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -365,7 +365,7 @@ int normalize_absolute_path(char *buf, const char *path)
  * path = Canonical absolute path
  * prefix_list = Colon-separated list of absolute paths
  *
- * Determines, for each path in parent_list, whether the "prefix" really
+ * Determines, for each path in prefix_list, whether the "prefix" really
  * is an ancestor directory of path.  Returns the length of the longest
  * ancestor directory, excluding any trailing slashes, or -1 if no prefix
  * is an ancestor.  (Note that this means 0 is returned if prefix_list is