Fix bug in erl_syntax.erl in two funs map_field_exact_value/1, map_field_assoc_value/1

There is an error while retrieving the value in functions:
* map_field_exact_value/1
* map_field_assoc_value/1

We give the name of the field as the value.

```erlang
-module(test).
-export([test/0]).
-compile([{parse_transform, portal_db_pt}]).

test() ->
    Value = 123,
    Result = #{ key => Value },
    Result.
```
AST for previous code:
```
[{attribute,1,file,{"src/test.erl",1}},
      {attribute,1,module,test},
      {attribute,1,lager_records,[]},
      {attribute,3,export,[{test,0}]},
      {attribute,5,compile,[]},
      {function,8,test,0,
          [{clause,8,[],[],
               [{match,9,{var,9,'Value'},{integer,9,123}},
                {match,10,
                    {var,10,'Result'},
                    {map,10,
                        [{map_field_assoc,10,{atom,10,key},{atom,10,key}}]}},
                {var,11,'Result'}]}]},
      {eof,12}]
```

```
[{map_field_assoc,10,{atom,10,key},{atom,10,key}}]}}, <--- this problem.
```

Typo in erl_syntax:map_field_exact_value/1 and erl_syntax:map_field_assoc_value/1:
```erlang
(data(Node))#map_field_exact.name <--- 
```