spapr-vscsi: fix CRQ status

Normally VIOSRP_OK (0) means success and non-zero value means error
except VIOSRP_OK2 (0x99) which is another success code by weird accident.

This uses 0 as success code always as some guests do not cope with
the 0x99 value well. The existing linux driver checks for both VIOSRP_OK
and VIOSRP_OK2 since 2.6.32.

This returns non-zero code (VIOSRP_ADAPTER_FAIL == 0x10) on errors which
can only happen if DMA write failed.
Suggested-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi/spapr_vscsi.c

@@ -195,9 +195,9 @@ static int vscsi_send_iu(VSCSIState *s, vscsi_req *req,
     req->crq.s.IU_data_ptr = req->iu.srp.rsp.tag; /* right byte order */
 
     if (rc == 0) {
-        req->crq.s.status = 0x99; /* Just needs to be non-zero */
+        req->crq.s.status = VIOSRP_OK;
     } else {
-        req->crq.s.status = 0x00;
+        req->crq.s.status = VIOSRP_ADAPTER_FAIL;
     }
 
     rc1 = spapr_vio_send_crq(&s->vdev, req->crq.raw);