SpinLockWait: Fixes unexpected lock success

With a contended unique lock, we forgot to reset the `Expected` value to
zero. This was causing a contended mutex to incorrectly succeed.

Noticed this when converting some pthread mutexes over to spinloops to
remove strace noise.

The reference wfe_mutex library I wrote didn't have this problem since
the implementation is slightly different.

FEXCore/Source/Utils/SpinWaitLock.h

@@ -259,6 +259,7 @@ namespace FEXCore::Utils::SpinWaitLock {
     do {
       // Wait until the futex is unlocked.
       Wait(Futex, 0);
+      Expected = 0;
     } while (!AtomicFutex->compare_exchange_strong(Expected, Desired));
   }