block: mark the bio as cloned in bio_iov_bvec_set

bio_iov_bvec_set clones the bio_vecs from the iter, and thus should be
treated like a cloned bio in every respect.  That also includes not
touching bi_max_vecs as that is a property of the bio allocation and not
its current payload.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>