virtio-scsi: Set _DRIVER_OK flag before scsi target scanning

Before we start scsi target scanning, we need to set the
VIRTIO_CONFIG_S_DRIVER_OK flag so the device can do setup properly.

This fix a bug when booting tcm_vhost with seabios.

Signed-off-by: Asias He <asias@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 5a7730db57ab0715223421e65b54fb50d6fefe5c)
diff --git a/src/virtio-scsi.c b/src/virtio-scsi.c
index ab74729..bf6c68b 100644
--- a/src/virtio-scsi.c
+++ b/src/virtio-scsi.c
@@ -147,6 +147,9 @@
         goto fail;
     }
 
+    vp_set_status(ioaddr, VIRTIO_CONFIG_S_ACKNOWLEDGE |
+                  VIRTIO_CONFIG_S_DRIVER | VIRTIO_CONFIG_S_DRIVER_OK);
+
     int i, tot;
     for (tot = 0, i = 0; i < 256; i++)
         tot += virtio_scsi_scan_target(pci, ioaddr, vq, i);
@@ -154,8 +157,6 @@
     if (!tot)
         goto fail;
 
-    vp_set_status(ioaddr, VIRTIO_CONFIG_S_ACKNOWLEDGE |
-                  VIRTIO_CONFIG_S_DRIVER | VIRTIO_CONFIG_S_DRIVER_OK);
     return;
 
 fail: