nouveau: Membar before between semaphore writes and the interrupt

nouveau: Membar before between semaphore writes and the interrupt

This ensures that the memory write and the interrupt are properly
ordered and we won't wake up the kernel before the semaphore write has
hit memory.

Fixes: b1ca384772b6 ("drm/nouveau/gv100-: switch to volta semaphore methods")
Cc: stable@vger.kernel.org
Signed-off-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://lore.kernel.org/r/20250829021633.1674524-2-airlied@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>