fix Mask-RCNN QAT bug (#5690)

ppdet/modeling/post_process.py

@@ -33,7 +33,7 @@ __all__ = [
 
 
 @register
-class BBoxPostProcess(nn.Layer):
+class BBoxPostProcess(object):
     __shared__ = ['num_classes', 'export_onnx']
     __inject__ = ['decode', 'nms']
 
@@ -45,7 +45,7 @@ class BBoxPostProcess(nn.Layer):
         self.nms = nms
         self.export_onnx = export_onnx
 
-    def forward(self, head_out, rois, im_shape, scale_factor):
+    def __call__(self, head_out, rois, im_shape, scale_factor):
         """
         Decode the bbox and do NMS if needed.