lsi: have lsi_request for the whole life time of the request.

Right now lsi_request is allocated when a request is queued and released
when a request is unqueued.  With this patch applied the lsi_request is
kept for the whole lifetime of the scsi request.

Rationale: We can use it for per-request data then.  The patch does that
already for the request tag.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>