SpeakerClustering: fix tensor dimennsions in forward()
For some paramters in SpeakerClustering.forward(), tensor dimensions were not specified and this resulted in zero dimension tensor inputs. This causes error when inferencing exported model in Triton server.

# What does this PR do ?

Avoids zero dimension input tensors. Also extracts values from the tensors which have single dim of size 1. This avoids scattered use of item() to extract value from tensor.

**Collection**: ASR Diarizer

# Changelog 
- Add specific line by line info of high level changes in this PR.

# Usage
Fix is needed to use exported clustering model in Triton

```python
# Add a code snippet demonstrating how to use this 
```

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**PR Type**:
- [ ] Bugfix

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# Additional Information
* Related to # (issue)
