Correctly determine ZERO_LEVEL_SPEC_DB_VAL which affects normalization for first signal buffer
# What does this PR do ?
If asr_model has preprocessor of type `AudioToMelSpectrogramPreprocessor`, `AudioToSpectrogram`, `AudioToMFCCPreprocessor`, etc., the `StreamingFeatureBufferer` incorrectly determines whether it uses log scale.

Instead of checking for 'log' attribute directly on preprocessor instance, it should check on the `preprocessor.featurizer` instance, which exposes the `log` property.

Therefore, the first few frames (until the generated silence is replaced by an actual audio signal) get incorrectly normalized and the model output is poor or absent.

First frame with incorrect `ZERO_LEVEL_SPEC_DB_VAL`:
![image](https://user-images.githubusercontent.com/8578790/228567021-62578f28-4b56-49b7-9f6b-952d0370d55b.png)


First frame with correct `ZERO_LEVEL_SPEC_DB_VAL`:
![image](https://user-images.githubusercontent.com/8578790/228566722-0cda3fe4-3a88-4c33-94fc-893ba4322680.png)

**Collection**: asr (`nemo.collections.asr.parts.utils.streaming_utils`)

# Changelog 
- `nemo.collections.asr.parts.utils.streaming_utils:365`
Checking for `asr_model.preprocessor.log` always resulted in False, as the `AudioToMelSpectrogramPreprocessor` doesn't define `log` property. Therefore I added an additional check for `asr_model.preprocessor.featurizer.log`.

**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


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