clang-format: Fix documentation generation

Summary:
It seems that the changes done to `ClangFormatStyleOptions.rst` @334408 are causing the generation of the documentation to fail, with the following error:

  Warning, treated as error:
    /llvm/tools/clang/docs/ClangFormatStyleOptions.rst:1060: WARNING: Definition list ends without a blank line; unexpected unindent.

This is due to missing indent in some code block, and fixed by this patch.

Reviewers: krasimir, djasper, klimek

Reviewed By: krasimir

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D48161

llvm-svn: 334709