qxl: reset update_surface

update init_qxl_ram to reset update_surface to 0. This fixes one case
of breakage when installing an old driver in a vm that had a new driver
installed. The newer driver would know about surface creation and would
change update_surface to !=0, then a reset would happen, all surfaces
are destroyed, then the old driver is initialized and issues an
UPDATE_AREA, and spice server aborts on invalid surface.

RHBZ: 690427
Signed-off-by: NAlon Levy <alevy@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/qxl.c

@@ -331,6 +331,7 @@ static void init_qxl_ram(PCIQXLDevice *d)
     d->ram->magic       = cpu_to_le32(QXL_RAM_MAGIC);
     d->ram->int_pending = cpu_to_le32(0);
     d->ram->int_mask    = cpu_to_le32(0);
+    d->ram->update_surface = 0;
     SPICE_RING_INIT(&d->ram->cmd_ring);
     SPICE_RING_INIT(&d->ram->cursor_ring);
     SPICE_RING_INIT(&d->ram->release_ring);