More prep work for immutable bvecs/effecient bio splitting - usage of
bi_vcnt has to be auditing, so getting rid of all the unnecessary usage
makes that easier.
Plus, bio_segments() is really what this code wanted, as it respects the
current value of bi_idx.
Signed-off-by: Kent Overstreet <koverstreet@google.com> CC: Jens Axboe <axboe@kernel.dk> CC: Eric Moore <Eric.Moore@lsi.com> CC: "James E.J. Bottomley" <JBottomley@parallels.com> CC: linux-scsi@vger.kernel.org