add missing return statement.

theano/sandbox/cuda/cuda_ndarray.cu

@@ -1214,6 +1214,8 @@ CudaNdarray_inplace_add_div(PyObject* py_self, PyObject * py_other, int fct_nb)
 static PyObject *
 CudaNdarray_inplace_add(PyObject* py_self, PyObject * py_other){
   CudaNdarray_inplace_add_div(py_self, py_other, 0);
+  Py_INCREF(py_self);
+  return py_self;
 }
 
 /*
@@ -1223,6 +1225,8 @@ CudaNdarray_inplace_add(PyObject* py_self, PyObject * py_other){
 static PyObject *
 CudaNdarray_inplace_div(PyObject* py_self, PyObject * py_other){
   CudaNdarray_inplace_add_div(py_self, py_other, 1);
+  Py_INCREF(py_self);
+  return py_self;
 }
 
 static PyNumberMethods CudaNdarrayNumberMethods =