drm/vmwgfx: Fixes to vmwgfx_fb

1.  When unsetting a mode, num_connector should be set to zero
2.  The pixel_format field needs to be initialized as newer DRM internal
    functions checks this field
3.  Take the drm_modeset_lock_all() because vmw_fb_kms_detach() can
    change current mode
Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_fb.c

@@ -434,7 +434,7 @@ static int vmw_fb_kms_detach(struct vmw_fb_par *par,
 		set.y = 0;
 		set.mode = NULL;
 		set.fb = NULL;
-		set.num_connectors = 1;
+		set.num_connectors = 0;
 		set.connectors = &par->con;
 		ret = drm_mode_set_config_internal(&set);
 		if (ret) {
@@ -822,7 +822,9 @@ int vmw_fb_off(struct vmw_private *vmw_priv)
 	flush_delayed_work(&par->local_work);
 
 	mutex_lock(&par->bo_mutex);
+	drm_modeset_lock_all(vmw_priv->dev);
 	(void) vmw_fb_kms_detach(par, true, false);
+	drm_modeset_unlock_all(vmw_priv->dev);
 	mutex_unlock(&par->bo_mutex);
 
 	return 0;