drm/amdgpu: not to save bo in the case of RAS err_event_athub

err_event_athub will corrupt VCPU buffer and not good to
be restored in amdgpu_vcn_resume() and in this case
the VCPU buffer needs to be cleared for VCN firmware to
work properly.

Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: David (Ming Qiang) Wu <David.Wu3@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>