drm/amdgpu: force completion for gpu reset

After all hw jobs are reset, hw fence is meaningless, so force_completion

Cc: William Lewis <minutemaidpark@hotmail.com>
Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>