[Ada] Spurious warning when using 'Type_Key on generic formal

gcc/ada/

	* sem_attr.adb (Type_Key): Avoid premature use warnings when the
	prefix is a generic actual.

gcc/ada/sem_attr.adb

@@ -6664,6 +6664,7 @@ package body Sem_Attr is
 
          if not Is_Frozen (Entity (P))
            and then not Is_Generic_Type (Entity (P))
+           and then not Is_Generic_Actual_Type (Entity (P))
          then
             Error_Msg_N ("premature usage of Type_Key?", N);
          end if;