drm/amd/display: Return the exact value for debugging

[Why]
It's unnecessary to set operation_result as invalid reply when
p_notify->result != AUX_RET_SUCCESS.

[How]
Set operation_result as p_notify->result to better understand
the reason for the error

Reviewed-by: Ray Wu <ray.wu@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>