databases/mariadb*: fix build ahead of CMake 3.20
All of the MariaDB releases contain the same ConnectorName CMake
module, and all of those copies of the module contain the same
syntax error. CMake < 3.20 ignores this and treats end() as
endif(), but this is an error in the upcoming version.
Specifically NOT bumping PORTREVISION because this is a build-only
fix that has no effect on the package.