virtio-gpu: fix ui idx check

Fix off-by-one value check (0 is the first scanout).
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 1463653560-26958-7-git-send-email-marcandre.lureau@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/display/virtio-gpu.c

@@ -879,7 +879,7 @@ static int virtio_gpu_ui_info(void *opaque, uint32_t idx, QemuUIInfo *info)
 {
     VirtIOGPU *g = opaque;
 
-    if (idx > g->conf.max_outputs) {
+    if (idx >= g->conf.max_outputs) {
         return -1;
     }