block: set BIO_NO_PAGE_REF in bio_iov_bvec_set

bio_iov_bvec_set assigns the foreign bvec, so setting the NO_PAGE_REF
directly there seems like the best fit.

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