smu firmware do not update response register immediately under
some delay tasks, we may read out the original value.

so need to clear the register before send smu message.
Acked-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NRex Zhu <Rex.Zhu@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>