drm/virtio: Fix same-context optimization

When VIRTGPU_EXECBUF_RING_IDX is used, we should be considering the
timeline that the EB if running on rather than the global driver fence
context.

Fixes: 85c83ea9 ("drm/virtio: implement context init: allocate an array of fence contexts")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20220812224001.2806463-1-robdclark@gmail.com


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>