Small fix to condvar->wait() return code

We want to return 0, not ETIMEDWAIT, if a wake_one/all() was consumed.
In one racy case, we returned the wrong one (we received a wakeup, but
still returned ETIMEDWAIT).

This probably doesn't matter at all in practice...

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>