sg_start_req(): use import_iovec()

			md->from_user = 0;

	}

	if (unlikely(iov_count > MAX_UIOVEC))

		return -EINVAL;

	if (iov_count) {

		int size = sizeof(struct iovec) * iov_count;

		struct iovec *iov;

		struct iovec *iov = NULL;

		struct iov_iter i;

		iov = memdup_user(hp->dxferp, size);

		if (IS_ERR(iov))

			return PTR_ERR(iov);

		res = import_iovec(rw, hp->dxferp, iov_count, 0, &iov, &i);

		if (res < 0)

			return res;

		iov_iter_init(&i, rw, iov, iov_count,

			      min_t(size_t, hp->dxfer_len,

				    iov_length(iov, iov_count)));

		iov_iter_truncate(&i, hp->dxfer_len);

		res = blk_rq_map_user_iov(q, rq, md, &i, GFP_ATOMIC);

		kfree(iov);