[Sema] Fix incorrect enum token namespace

Summary:
This patch fix the scoping of enum literal. They were not resolving
to the right type.

It was not causing any problem as one is a copy of the other one.

The literal in the switch are resolving to Sema.h:5527
```
  enum AccessResult {
    AR_accessible,
    AR_inaccessible,
    AR_dependent,
    AR_delayed
  };
```

Instead of SemaAccess.cpp:27
```
/// A copy of Sema's enum without AR_delayed.
enum AccessResult {
  AR_accessible,
  AR_inaccessible,
  AR_dependent
};
```

This issue was found by a new clang-tidy check (still on-going).

Reviewers: rsmith, aaron.ballman

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20773

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@271431 91177308-0d34-0410-b5e6-96231b3b80d8