GEOS-Chem submod update: Merge PR #2176 (UCX bug fixes )

This commit informs the GCHP superproject about the following
commits that were pushed to the GitHub geos-chem/geos-chem repository:

5f81b6555 Merge PR #2176 (UCX bug fixes)

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>