panfrost: Drop rasterizer null checks in draw calls

panfrost: Drop rasterizer null checks in draw calls

rasterizer must be non-null when draw_vbo is called (indeed, we assert
this there), so anything in the per-draw graphics path can safely assume
we have a rasterizer object bound.

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/6327>