lavapipe: enable alpha to one.

CTS seems fine with this.

Cc: 20.3 <mesa-stable>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7499>
(cherry picked from commit a04a146560717014937d9e13ad24eb33cb6f0a44)
2 files changed