clang-format: Fix incorrect cast detection.

Before:
  auto s = sizeof...(Ts)-1;

After:
  auto s = sizeof...(Ts) - 1;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@272536 91177308-0d34-0410-b5e6-96231b3b80d8