message: append: fix unused variable warning

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I26e542e7acdac08e143fe15ad50a2d570ff9ea5d
diff --git a/include/sdbusplus/message/append.hpp b/include/sdbusplus/message/append.hpp
index 5dd8645..dd002a5 100644
--- a/include/sdbusplus/message/append.hpp
+++ b/include/sdbusplus/message/append.hpp
@@ -183,7 +183,7 @@
 struct append_single<details::unix_fd_type>
 {
     template <typename T>
-    static void sanitize(const T& s)
+    static void sanitize(const T&)
     {}
 
     template <typename T>