[oneDNN] Fixing a failure in mkl_fused_batch_norm_op_test
This PR fixes a failure in a test that was enabled recently by this [PR](https://github.com/tensorflow/tensorflow/commit/155b34bad741124f778978f806d82551f9d35a66). The reference values are slightly changed due to use of different gemm-api. That resulted in a one value mismatch. So we are updating the test by adding relative error tolerance.