st/nine: Fix leak at device destruction

st/nine: Fix leak at device destruction

At the release of the last object holding a reference
on the device, the device dtor was executed and
the objector dtor was ignored.

The proper way is to execute the object dtor, then
the device dtor.

The previous code was likely for a workaround against
something that was fixed since.

Signed-off-by: Axel Davy <davyaxel0@gmail.com>
Acked-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9177>