drm/crtc: fix uninitialized variable use even harder

DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
which means we can't rely too much on variable initializers.

Fixes: 6e455f5d

 ("drm/crtc: fix uninitialized variable use")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # sc7180, sdm845
Link: https://patchwork.freedesktop.org/patch/msgid/20240212215534.190682-1-robdclark@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>