Use as_pointer rather than to_native

Author: chrisseaton

lib/truffle/truffle/fiddle_backend.rb

@@ -84,7 +84,7 @@ def self.convert_native_to_ruby(type, val)
     when Fiddle::TYPE_VOID
       nil
     when Fiddle::TYPE_VOIDP
-      Fiddle::Pointer.new(Truffle::Interop.to_native(val))
+      Fiddle::Pointer.new(Truffle::Interop.as_pointer(val))
     when Fiddle::TYPE_INT, Fiddle::TYPE_FLOAT, Fiddle::TYPE_DOUBLE
       val
     else