add trans rule Placeholder->Data for parser

parser/common/op_map.cc

@@ -82,6 +82,7 @@ FMK_FUNC_HOST_VISIBILITY FMK_FUNC_DEV_VISIBILITY std::map<std::string, std::stri
 
 FMK_FUNC_HOST_VISIBILITY FMK_FUNC_DEV_VISIBILITY map<string, string> tensorflow_train_op_map = {
     {"BroadcastGradientArgs", BROADCASTGRADIENTARGS},
+    {"Placeholder", DATA},
     {"StopGradient", STOPGRADIENT},
     {"ExpandDims", EXPANDDIMS},
     {"DestroyTemporaryVariable", DESTROYTEMPORARYVARIABLE},