d20200109_HIRANO_PDB ports different in ports and data 

I think I have discovered an inconsistency in the `d20200109_HIRANO_PDB` dataset:
```
ds = csr_dataset("d20200109_HIRANO_PDB")

unique(ds$ports$CSR_PORT) # gives 0
unique(ds$data$CSR_PORT) # gives 1 2 3 4 5 6
```
To my mind, all ports should be referenced in ports, so that the user knows which `CSR_MSMT_VAR` they are looking at.

Thanks for putting this great effort together!