block: Switch to using refcount_t for zone write plugs

Replace the raw atomic_t reference counting of zone write plugs with a
refcount_t.  No functional changes.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202411050650.ilIZa8S7-lkp@intel.com/


Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241107065438.236348-1-dlemoal@kernel.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>