[DOC] Fix the table in Improving accuracy with INC

[anko-intel]

Description

Fix formating of the table in https://mxnet.apache.org/versions/master/api/python/docs/tutorials/performance/backend/dnnl/dnnl_quantization_inc.html

[mxnet-bot]

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[anko-intel]

@mxnet-bot run ci [unix-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [unix-gpu]