[CodeComplete] Fix accessibilty of protected members from base class.

Summary:
Currently, protected members from base classes are marked as
inaccessible when completing in derived class. This patch fixes the problem by
setting the naming class correctly when looking up results in base class
according to [11.2.p5].

Reviewers: aaron.ballman, sammccall, rsmith

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D49421

llvm-svn: 337453