venus: properly initialize ring monitor initial alive status

venus: properly initialize ring monitor initial alive status

This avoids a potential race condition if two threads are competing for
the monitor with the initial states, and the losing one may run into
alive status being false and abort.

Fixes: 4a4b05869a6 ("venus: check and configure new ringMonitoring feature")
Signed-off-by: Yiwei Zhang <zzyiwei@chromium.org>
Reported-by: Lina Versace <lina@kiwitree.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26179>
(cherry picked from commit 8ac7d78bf3512aa7575f9c8595494ea592ab2e58)