xfs_repair: set exit code correctly when zones are inconsistent

Although xfs_validate_zone() will print exactly what's wrong with a zone
to the console, repair still needs to print something via do_warn so
that we set the exit code correctly.

While we're at it, correct the lack of libxfs namespacing to shut up
xfs/437.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>