Simplified SourceManager::translateLineCol a bit.

Reviewers: rsmith

Reviewed By: rsmith

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1183

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187386 91177308-0d34-0410-b5e6-96231b3b80d8