drm/msm/gem: Drop obj lock in msm_gem_free_object()

The only reason we grabbed the lock was to satisfy a bunch of places
that WARN_ON() if called without the lock held.  But this angers lockdep
which doesn't realize no one else can be holding the lock by the time we
end up destroying the object (and sees what would otherwise be a locking
inversion between reservation_ww_class_mutex and fs_reclaim).

Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/14


Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/489364/
Link: https://lore.kernel.org/r/20220613205032.2652374-1-robdclark@gmail.com