Fix a typo in pkt_start_recovery.

Fixes: 74d46992 ("block: replace bi_bdev with a gendisk pointer and partitions index")
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>