llvmpipe: ignore multisample state for alpha_to_one

this is more accurate and fixes usage with lavapipe

cc: mesa-stable

Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17627>
1 file changed