clang-format: Fix unary operator detection in for loops.

Before:
  for (;; * a = b) {}

After:
  for (;; *a = b) {}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@242849 91177308-0d34-0410-b5e6-96231b3b80d8