reformat source code

according to code styles, 'AccessModifierOffset' should be -2.

src/sql/resolver/expr/ob_var_expr.h

@@ -23,7 +23,7 @@ namespace expr {
 
 // OceanBase constant expression.
 class ObVarExpr : virtual public ObExpr {
-  public:
+public:
   ObVarExpr()
   {
     set_expr_class(EXPR_VAR);