drm/atomic-helper: Change parameter name of drm_atomic_helper_cleanup_planes()

drm/atomic-helper: Change parameter name of drm_atomic_helper_cleanup_planes()

drm_atomic_helper_cleanup_planes() is one of the final part of a commit,
and will free up all plane resources used in the previous commit.  It
takes the drm_atomic_state being committed as a parameter.

However, that parameter name is called (and documented) as old_state,
which is pretty confusing. Let's rename that variable as state.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20250213-bridge-connector-v3-24-e71598f49c8f@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>