CFG.cpp: Fix wrapping logic when printing block preds/succs.

First check only wrapped with i==8, second wrapped at i==2,8,18,28,...
This fix restores the intended behavior: i==8,18,28,...

Found with -fsanitize=integer.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171718 91177308-0d34-0410-b5e6-96231b3b80d8