drm/amdgpu/vcn1: add cancel_delayed_work_sync before power gate

drm/amdgpu/vcn1: add cancel_delayed_work_sync before power gate

commit b95f045ea35673572ef46d6483ad8bd6d353d63c upstream.

Add cancel_delayed_work_sync before set power gating state
to avoid race condition issue when power gating.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>