Fix typos in block yml (io_ports)

[eltos]

Pull Request Details

Fixes the typos io_port -> io_ports

Description

Related Issue

Which devices/areas does this affect?

Custom RFNoC blocks based on the RFNoC gain example YML template as described in the tutorial https://kb.ettus.com/Getting_Started_with_RFNoC_in_UHD_4.0

Testing Done

Checklist

• [x] I have read the CONTRIBUTING document.
• [x] My code follows the code style of this project. See CODING.md.
• I have updated the documentation accordingly.
• I have added tests to cover my changes, and all previous tests pass.
• I have checked all compat numbers if they need updating (FPGA compat, MPM compat, noc_shell, specific RFNoC block, ...)

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