libxl: colo: add missing break in qemu_disk_scsi_drive_string

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/libxl_dm.c

@@ -816,6 +816,7 @@ static char *qemu_disk_scsi_drive_string(libxl__gc *gc, const char *target_path,
             "file.backing.file.filename=%s,"
             "file.backing.backing=%s",
             unit, active_disk, hidden_disk, exportname);
+        break;
     default:
          abort();
     }