Add PolyKinds to Clash.Class.BitPack.Internal

This gives us `BitPack` instances for `Proxy a` where `a` is a Kind from our derived `BitPack` instance for `Proxy a`

Author: lmbollen

clash-prelude/src/Clash/Class/BitPack/Internal.hs

@@ -12,7 +12,7 @@ Maintainer :  QBayLogic B.V. <[email protected]>
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-}
-
+{-# LANGUAGE PolyKinds #-} -- Required for BitPack (KnownNat n) => BitPack (Proxy n) instances
 {-# LANGUAGE Trustworthy #-}
 
 {-# OPTIONS_GHC -fplugin=GHC.TypeLits.Extra.Solver #-}