mariadb: fix tarball fetch URL

http://mirror.stshosting.co.uk/mariadb responds with a 404 error, so
use http://archive.mariadb.org

 instead.

Signed-off-by: Mario Domenech Goulart <mario@ossystems.com.br>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>