Change SyncBN to BN for qat_faster_rcnn_fbnetv3a_C4.yaml

Summary:
fixes https://github.com/facebookresearch/d2go/issues/27

Pull Request resolved: https://github.com/facebookresearch/d2go/pull/28

Reviewed By: newstzpz

Differential Revision: D27214440

Pulled By: zhanghang1989

fbshipit-source-id: da538ad1e29faa9c36065db89138b1cc97045a28

configs/qat_faster_rcnn_fbnetv3a_C4.yaml

@@ -11,3 +11,8 @@ QUANTIZATION:
     ENABLE_OBSERVER_ITER: 0
     DISABLE_OBSERVER_ITER: 5
     FREEZE_BN_ITER: 7
+MODEL:
+  FBNET_V2:
+    NORM: "bn"
+  ROI_BOX_HEAD:
+    NORM: "bn"