Fix staking key hash message

When deriving an address with a foreign staking key Trezor would crash
due to forgotten `decode()` on hexlified staking key hash which was to
be displayed.

This wasn't discovered while testing because it weirdly would pass with
a `aaff00` string, but not with longer ones.

core/src/apps/cardano/layout.py

@@ -202,7 +202,7 @@ async def show_warning_address_foreign_staking_key(
             address_n_to_str(staking_account_path),
         )
     else:
-        staking_key_message = ("Staking key:", hexlify(staking_key_hash))
+        staking_key_message = ("Staking key:", hexlify(staking_key_hash).decode())
 
     await show_warning(
         ctx, staking_key_message, button="Ok",