virgl: fix checking fences

virgl: fix checking fences

When calling virgl_fence_wait() with timeout=0,
virgl_{drm,vtest}_resource_is_busy() is called. However, it returns TRUE
for a busy resource, whereace virgl_fence_wait() should return TRUE for
a completed (non-busy) resource.

This fixes running supertuxkart in a VM (I could not reproduce locally
with vtest though there is a similar fix)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Cc: "11.1 11.2 12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>