drm/vmwgfx: fix a NULL dereference

We dereference "eaction->event" inside the call to drm_send_event_locked()
so should hold off on setting it to NULL until afterward.

Fixes: fb740cf2 ("drm: Create drm_send_event helpers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160128090646.GA5824@mwandaSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/vmwgfx/vmwgfx_fence.c

@@ -880,8 +880,8 @@ static void vmw_event_fence_action_seq_passed(struct vmw_fence_action *action)
 	}
 
 	list_del_init(&eaction->fpriv_head);
-	eaction->event = NULL;
 	drm_send_event_locked(dev, eaction->event);
+	eaction->event = NULL;
 	spin_unlock_irqrestore(&dev->event_lock, irq_flags);
 }