gallium: fix missing bit field in p_state.h

Marek pointed this out, not sure how we missed it.

Fixes: 3dc6da1ac1f5 ("gallium: add a non-multisample sample mask out behaviour flag.")

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7741>
(cherry picked from commit 105fc1c615eb4963503c738c68766f830bc5a662)
2 files changed