s390x: fix -drive in the absence of aliases

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

blockdev.c

diff --git a/blockdev.c b/blockdev.c
index 7e4c548..7d7ac31 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -565,7 +565,11 @@
     case IF_VIRTIO:
         /* add virtio block device */
         opts = qemu_opts_create(qemu_find_opts("device"), NULL, 0);
-        qemu_opt_set(opts, "driver", "virtio-blk");
+        if (arch_type == QEMU_ARCH_S390X) {
+            qemu_opt_set(opts, "driver", "virtio-blk-s390");
+        } else {
+            qemu_opt_set(opts, "driver", "virtio-blk-pci");
+        }
         qemu_opt_set(opts, "drive", dinfo->id);
         if (devaddr)
             qemu_opt_set(opts, "addr", devaddr);