'PerfEngine' object has no attribute 'pre_compile_config' when the get_best_batch_size() implemented in the backend

[jackzipu]

After implemented the get_best_batch_size() to return a list of batch sizes, got the following error:

Traceback (most recent call last):
  File "byte_mlperf/core/perf_engine.py", line 376, in <module>
    engine.start_engine()
  File "byte_mlperf/core/perf_engine.py", line 90, in start_engine
    status, workload_report = self.single_workload_perf(self.workload)
  File "byte_mlperf/core/perf_engine.py", line 155, in single_workload_perf
    self.pre_compile_config['workload']['batch_sizes'] = best_batch_sizes
AttributeError: 'PerfEngine' object has no attribute 'pre_compile_config'

The following codes

        best_batch_sizes = self.compile_backend.get_best_batch_size()
        if isinstance(best_batch_sizes, list):
            self.pre_compile_config['workload'][
                'batch_sizes'] = best_batch_sizes

should be:

        best_batch_sizes = self.compile_backend.get_best_batch_size()
        if isinstance(best_batch_sizes, list):
            pre_compile_config['workload'][
                'batch_sizes'] = best_batch_sizes

[JianzheXiao]

Fixed