parse.y: Fix the locations of NODE_DVAR and NODE_LVAR

* parse.y: Fix the locations of NODE_DVAR and NODE_LVAR
    when it's a multiple assignment method parameter.

  e.g. The locations of NODE_DVAR is fixed:

  ```
  a {|(b, c)| d}
  ```

  * Before

  ```
  NODE_DVAR (line: 1, first_lineno: 1, first_column: 4, last_lineno: 1, last_column: 10)
  ```

  * After

  ```
  NODE_DVAR (line: 1, first_lineno: 1, first_column: 5, last_lineno: 1, last_column: 9)
  ```

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60836 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

parse.y

@@ -4640,10 +4640,10 @@ f_arg_item	: f_arg_asgn
 			arg_var(tid);
 		    /*%%%*/
 			if (dyna_in_block()) {
-			    $2->nd_value = new_dvar(tid, &@$);
+			    $2->nd_value = new_dvar(tid, &@2);
 			}
 			else {
-			    $2->nd_value = new_lvar(tid, &@$);
+			    $2->nd_value = new_lvar(tid, &@2);
 			}
 			$$ = NEW_ARGS_AUX(tid, 1);
 			$$->nd_next = $2;