[Chronik] Fix CARGO_BUILD_DIR, incorrectly based on CMAKE_CURRENT_BINARY_DIR instead of CMAKE_BINARY_DIR

Summary:
CARGO_BUILD_DIR is the path where the cxx crate generates the bridging sources.
We've incorrectly used CMAKE_CURRENT_BINARY_DIR instead of CMAKE_BINARY_DIR, and this fixes it.

Test Plan: ninja check-crates

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11862