drm/amdgpu/vpe: cancel delayed work in hw_fini

We need to cancel any outstanding work at both suspend
and driver teardown. Move the cancel to hw_fini which
gets called in both cases.

Reviewed-by: David (Ming Qiang) Wu <David.Wu3@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>