Another warning fix for GCC from Thomas Klausner.

utf8.c

@@ -72,7 +72,7 @@ static u_int utf8_next_index;
 
 /* Get a UTF-8 item from data. */
 static struct utf8_item *
-utf8_item_by_data(const char *data, size_t size)
+utf8_item_by_data(const u_char *data, size_t size)
 {
 	struct utf8_item	ui;