[chronik] Use the chronik category for logging chronik broadcast errors

Summary: If a block notification fails to be sent by chronik, the log message should use the chronik log category.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18070