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

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.

Cc: stable@vger.kernel.org
Fixes: 5ab829f1971d ("md/md-llbitmap: introduce new lockless bitmap")
Link: https://lore.kernel.org/linux-raid/20260223024038.3084853-3-yukuai@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>