LU-13004 osp: use KIOV in osp_prep_update_req

LU-13004 osp: use KIOV in osp_prep_update_req

Convert osp_prep_update_req to use a BULK_BUF_KIOV
rather than a BULK_BUF_KVEC descriptor.

This is a step towards remove KIOV support.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I2fdf84d73ba2d34c678b6eb6a8bbd323a761dfe4
Reviewed-on: https://review.whamcloud.com/36828
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>