Use 'unsigned short' for mode, like diff_filespec does

struct diff_filespec defines mode to be an 'unsigned short'.  Several
other places in the API which we'd like to interact with using a
diff_filespec used a plain unsigned (or unsigned int).  This caused
problems when taking addresses, so switch to unsigned short.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

notes.c

@@ -986,7 +986,7 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
 		combine_notes_fn combine_notes, int flags)
 {
 	struct object_id oid, object_oid;
-	unsigned mode;
+	unsigned short mode;
 	struct leaf_node root_tree;
 
 	if (!t)