clang-format: Fixes spaces in case statements.

This fixes llvm.org/PR19482.

Before:
  switch (a) {
    case(B) :
      return;
  }

After:
  switch (a) {
    case (B):
      return;
  }

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207402 91177308-0d34-0410-b5e6-96231b3b80d8