scsi-disk: Clear aiocb on read completion

Once the I/O completion callback returned, aiocb will be released by the
controller. So we have to clear the reference not only in
scsi_write_complete, but also in scsi_read_complete. Otherwise we risk
inconsistencies when a reset hits us before the related request is
released.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/scsi-disk.c

@@ -125,6 +125,8 @@ static void scsi_read_complete(void * opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
 
+    r->req.aiocb = NULL;
+
     if (ret) {
         DPRINTF("IO error\n");
         r->req.bus->complete(r->req.bus, SCSI_REASON_DATA, r->req.tag, 0);