Fix mysql-configmap.yaml error

Author: Mengjiao Liu

content/en/examples/application/mysql/mysql-configmap.yaml

@@ -9,8 +9,10 @@ data:
     # Apply this config only on the primary.
     [mysqld]
     log-bin
+    datadir=/var/lib/mysql/mysql
   replica.cnf: |
     # Apply this config only on replicas.
     [mysqld]
     super-read-only
+    datadir=/var/lib/mysql/mysql