Update links to finn-base repo

[senekor]

finn-base seems to be deprecated and the pointed-to files now have equivalents in the finn repo.

[auphelia]

Hi @senekor,
Thank you for your PR! Good catch with the outdated links.
Could you please sign-off your commit? To be compliant with our contribution guidelines: https://github.com/Xilinx/finn/blob/main/CONTRIBUTING.md
It should be possible to sign-off already pushed commits.

[senekor]

@auphelia done 🙂

[auphelia]

Thank you @senekor !