[SCSI] libosd: Let _osd_req_finalize_data_integrity receive number of out_bytes

_osd_req_finalize_data_integrity was trying to deduce the number of
out_bytes from passed osd_request->out.bio. This is wrong when
the bio is chained. The caller of _osd_req_finalize_data_integrity
has more ready available information and should just pass it.

Also in the light of future support for CDB-continuation segment this is
a better solution.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>