drm/amd/display: Fix DCN3 B0 DP Alt Mapping

[Why]
DCN3 B0 has a mux, which redirects PHYC and PHYD to PHYF and PHYG.

[How]
Fix DIG mapping.

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Zhan Liu <Zhan.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>