ilo: unref old fence
ilo: unref old fence

Some, but not all, state trackers will explicitly unref (and set to
NULL) the previous *fence before calling pipe->flush().  So driver
should use fence_ref() which will unref the old fence if not NULL.

Signed-off-by: Rob Clark <6f78cdb10adbe0a7fbbf4098125a51f401c77a5f@freedesktop.org>
Acked-by: Chia-I Wu <1c78ba4519acc7012ab6d28d2e5ef6630c8f0d2e@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler