add missing return to GpuFromHost R_op

theano/sandbox/cuda/basic_ops.py

@@ -152,7 +152,7 @@ class GpuFromHost(GpuOp):
 
     def R_op(self, inputs, eval_points):
         ev, = eval_points
-        [self(ev)]
+        return [self(ev)]
 
     def infer_shape(self, node, xshp):
         return xshp