mariadb: mariadb-server depends on mariadb-client

/etc/init.d/mysqld from mariadb-server uses mysqladmin, which is installed
into mariadb-client, so add the dependency to make this script be able
to run

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>