[PATCH] WorkStruct: Use direct assignment rather than cmpxchg()

Use direct assignment rather than cmpxchg() as the latter is unavailable
and unimplementable on some platforms and is actually unnecessary.

The use of cmpxchg() was to guard against two possibilities, neither of
which can actually occur:

 (1) The pending flag may have been unset or may be cleared.  However, given
     where it's called, the pending flag is _always_ set.  I don't think it
     can be unset whilst we're in set_wq_data().

     Once the work is enqueued to be actually run, the only way off the queue
     is for it to be actually run.

     If it's a delayed work item, then the bit can't be cleared by the timer
     because we haven't started the timer yet.  Also, the pending bit can't be
     cleared by cancelling the delayed work _until_ the work item has had its
     timer started.

 (2) The workqueue pointer might change.  This can only happen in two cases:

     (a) The work item has just been queued to actually run, and s...