Fix bug for mssql (#1854)

Reviewed-on: https://gitea.com/xorm/xorm/pulls/1854
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-committed-by: Lunny Xiao <xiaolunwen@gmail.com>

dialects/mssql.go

@@ -220,6 +220,8 @@ type mssql struct {
 
 func (db *mssql) Init(uri *URI) error {
 	db.quoter = mssqlQuoter
+	db.defaultChar = "CHAR"
+	db.defaultVarchar = "VARCHAR"
 	return db.Base.Init(db, uri)
 }