[Dy2St]Fix is_paddle_func not take effect for plain paddle API (#51585)

* Fix is_paddle_func not take effect for plain paddle API

* fix typo

* fix typo

python/paddle/fluid/tests/unittests/dygraph_to_static/test_convert_call.py

@@ -270,6 +270,7 @@ class TestNotToConvert2(TestRecursiveCall2):
 
 
 # Situation 3 : test to_static for paddle api
+@paddle.jit.not_to_static
 def forward(self, x):
     if x.shape[0] > 1:
         x = x + 1

python/paddle/jit/dy2static/utils.py

@@ -327,19 +327,15 @@ def is_paddle_func(func, ignore_white_list=True):
             func = func.func
 
         func_name = getattr(func, '__name__', None)
-        # In case of dynamically monkey patch customised function
-        # into paddle class obj, so we consider its class module
-        # path as prefix.
-        if hasattr(func, "__self__"):
-            func = func.__self__
-            func_name = func.__class__.__name__
-        elif inspect.ismethod(func):
+        if inspect.ismethod(func):
+            func_name = func.__self__.__class__.__name__
             func = func.__func__
 
         m = inspect.getmodule(func)
         flag = m is not None and m.__name__.startswith(PADDLE_MODULE_PREFIX)
         if ignore_white_list:
             flag = flag and not in_white_list(m, func_name)
+
         return flag
     except Exception:
         return False