Fix incorrect assignment for nodeid in TransactionIdGetCommitTsData()

Hi hackers,

This is my first patch
There is an incorrect assignment of nodeid = 0 in 
TransactionIdGetCommitTsData() (commit_ts.c).
Elsewhere in the file, the code consistently uses InvalidReplOriginId.
Even though InvalidReplOriginId also evaluates to 0, it should be used 
here for clarity and consistency.

Best regards,
Wang Peng