drm/amdgpu: Cancel the delay work when suspend

Cancel the delay work to avoid the corner case that
ib test was not running when suspend

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>