[Why]
In dm_dp_aux_transfer() now, we forget to handle AUX_WR fail cases. We
suppose every write wil get done successfully and hence some AUX
commands might not sent out indeed.

[How]
Check if AUX_WR success. If not, retry it.
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>