Stacking drivers may append bvecs to existing bio's, resulting
in non-zero bi_idx conditions.  This patch counts the loops of
bio_for_each_segment() rather than inheriting the bi_idx value
to pass as a segment count to the hardware submission routine.
Signed-off-by: NSam Bradshaw <sbradshaw@micron.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>