clang-format: don't indent namespaces

This change doesn't affect existing code. Inner namespace indentation
can lead to a lot of indentation in the case of anonymous namespaces and
the like, impeding readability. Of the clang-format builtin styles
LLVM, Google, Chromium and Mozilla use None while WebKit uses Inner.

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>