MDEV-12096: Fix ln syntax in debian/rules for libmariadb3 symlink creation
MDEV-12096: Fix ln syntax in debian/rules for libmariadb3 symlink creation

Compatibility links ended up looking like this:
libmysqlclient.so.18 -> /tmp/buildd/mariadb-10.2-10.2.0/debian/tmp/usr/lib/i386-linux-gnu/libmariadb.so.3

This change fixes ln syntax to create links with correct target paths.

natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2