Deb: Fix libmariadbclient.so.18 link path to point to libmariadb.so.3

As libmariadb.so.3 does not reside in a multi-arch directory (yet),
use the plain path.

debian/rules

@@ -158,7 +158,7 @@ override_dh_auto_install:
 	install -D -m 644 debian/mariadb-server-10.2.py $(TMP)/usr/share/apport/package-hooks/source_mariadb-10.2.py
 
 	# Install libmariadbclient18 compatibility links
-	ln -s /usr/lib/$(DEB_HOST_MULTIARCH)/libmariadb.so.3 $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadbclient.so.18
+	ln -s /usr/lib/mariadb/libmariadb.so.3 $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadbclient.so.18
 
 	touch $@