[libc] fix rwlock test (#100962)

Previous commit uses wrong clock id and forget to release an additional
rdlock. cc @Eric977
Sorry for missing this in my initial review.

Fixes https://github.com/llvm/llvm-project/issues/100960.

Notice that the timestamp is created via
```c++
  LIBC_NAMESPACE::clock_gettime(CLOCK_REALTIME, &ts);
  ts.tv_nsec += 50'000;
  if (ts.tv_nsec >= 1'000'000'000) {
    ts.tv_nsec -= 1'000'000'000;
    ts.tv_sec += 1;
  }
```

0 files changed, 0 insertions, 0 deletions