Revert "drm/amd/display: setting the DIG_MODE to the correct value."

This reverts commit 385857ad.

Reason for revert: Root cause of this issue is found. The workaround is not needed anymore.

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>