`StopIteration` Exception in Conformer Encoder because of `next(self.parameters())`
Hi, I get `StopIteration` exception here:

https://github.com/NVIDIA/NeMo/blob/41f27a5e68934761b05dd373e7b288aa798858e5/nemo/collections/asr/modules/conformer_encoder.py#L231

I call this method from `forward_for_export` here:

https://github.com/NVIDIA/NeMo/blob/41f27a5e68934761b05dd373e7b288aa798858e5/nemo/collections/asr/modules/conformer_encoder.py#L249

I found that `self.parameters()` is zero length. Found this happens when I use multiple GPUs in DP mode. When I run the code on one GPU I get `self.parameters() > 0`.

Issue about it: https://github.com/pytorch/pytorch/issues/40457

Maybe it would be better if the device was passed into the method, like so:
```
def set_max_audio_length(self, max_audio_length, device='cpu'):
    ....
```

Because it's strange to get such problems when getting a device, when it can be easily passed as a parameter.
