drm/amdgpu: use dma_fence_chain_contained

Instead of manually extracting the fence.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204100429.2049-7-christian.koenig@amd.com