[SCSI] libosd: Free resources in reverse order of allocation

At osd_end_request first free the request that might
point to pages, then free these pages. In reverse order
of allocation. For now it's just anal neatness. When we'll
use mempools It'll also pay in performance.

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