Merge #11469: fix typo in comment of chain.cpp

Summary:
f902e40 fix typo in comment of chain.cpp (Johannes Kanig)

Pull request description:

Tree-SHA512: 1af049bd75f244febc2c249f7b743b481ed6ce935f1f5265881f57064d69e0f055b9334dae765132348125a5e688f99b07a255de7deacf37ac57d1e6966b5e4b

Backport of Core PR11469
https://github.com/bitcoin/bitcoin/pull/11469

Test Plan:

make check

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3659