change cache_call_signatures, so that it has a well defined input.

jedi/api/__init__.py

@@ -545,8 +545,7 @@ class Script(object):
             return []
 
         with common.scale_speed_settings(settings.scale_call_signatures):
-            _callable = lambda: self._evaluator.eval_call(call)
-            origins = cache.cache_call_signatures(_callable, self.source,
+            origins = cache.cache_call_signatures(self._evaluator, call, self.source,
                                                   self._pos, user_stmt)
         debug.speed('func_call followed')