block: Don't call bdrv_eject() if the tray state didn't change

It's not needed. Besides we can then assume that bdrv_eject() is
only called when there's a tray state change, which is useful to
the DEVICE_TRAY_MOVED event (going to be added in a future
commit).

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
index a5d2fd1..091ecdc 100644
--- a/hw/scsi-disk.c
+++ b/hw/scsi-disk.c
@@ -1050,8 +1050,11 @@
                                  : SENSE_CODE(NOT_READY_REMOVAL_PREVENTED));
             return -1;
         }
-        bdrv_eject(s->qdev.conf.bs, !start);
-        s->tray_open = !start;
+
+        if (s->tray_open != !start) {
+            bdrv_eject(s->qdev.conf.bs, !start);
+            s->tray_open = !start;
+        }
     }
     return 0;
 }