panfrost: Use opaque pack for vertex shaders

Not much difference but eliminates a reference to shader_meta (and
avoids a memcpy but who cares).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6440>
1 file changed