md/md-llbitmap: raise barrier before state machine transition

In the Linux kernel, the following vulnerability has been resolved: md/md-llbitmap: raise barrier before state machine transition Move the barrier raise operation before calling llbitmap_state_machine() in both llbitmap_start_write() and llbitmap_start_discard(). This ensures the barrier is in place before any state transitions occur, preventing potential race conditions where the state machine could complete before the barrier is properly raised.