Fix typo in comparison in clang_CXCursorSet_contains().

Fixes PR 10124.

Patch by Jens Kilian.

Thanks to Nikola Smiljanic for following up.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@180177 91177308-0d34-0410-b5e6-96231b3b80d8