virgl: Fix pipe_resource leaks under multi-sample.

Fixes: 900a80f9 ("virgl: virgl_transfer should own its virgl_resource")

Signed-off-by: Lepton Wu <lepton@chromium.org>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
22 jobs for !1881 with leak in 13 minutes and 47 seconds (queued for 3 seconds)
merge request