[SCSI] libosd: Fix unchecked err return found by smatch

Doing CHECK="smatch --two-passes gives:
drivers/scsi/osd/osd_initiator.c +1435 osd_finalize_request warning: assignment to 'ret' was never used

Which is an unchecked possible allocation failure, Fixed.

Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>