[clang-format] Fix documentation for SpaceAfterCStyleCast option

Patch contributed by @EricMarti!

Summary: I noticed that the example for SpaceAfterCStyleCast does not match its description. I fixed the example after testing it out.

Reviewers: rsmith, krasimir

Reviewed By: krasimir

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D43731

llvm-svn: 326781