update readability-identifier-naming-objc test to use interface ivar....

update readability-identifier-naming-objc test to use interface ivar. Implementation ivars are not supported in 32-bits OS.

Reviewers: alexfh, chandlerc

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D45936

llvm-svn: 330562