drm/nouveau: Check dma_fence in canonical way

In nouveau_fence_done(), a fence is checked for being signaled by
manually evaluating the base fence's bits. This can be done in a
canonical manner through dma_fence_is_signaled().

Replace the bit-check with dma_fence_is_signaled().

Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://lore.kernel.org/r/20250424130254.42046-6-phasta@kernel.org


Signed-off-by: Danilo Krummrich <dakr@kernel.org>