[BNNS] Speech Commands example doesn't work

[Christywl]

Test Env:
Chromium Version: nightly build 75.0.3739.0 (79fdab0)
Platform: macOS

Expected Result:
Speech Commands should work.

Actual Result:
Speech Commands example doesn't work.

How to Reproduce:

1. Launch chromium and visit https://intel.github.io/webml-polyfill/examples/speech_commands/
2. Select FAST_SINGLE_ANSWER
3. Select KWS CNN model