drm/amd/display: fix global sync param extraction indexing

dcn20_calculate_dlg_params was incorrectly indexing pipe src and
dst structs when extracting global sync params.

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Jaehyun Chung <Jaehyun.Chung@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>