drm/amd/display: cap dpp dto phase not more than modulo.

[Why]
4K monitor shows corruption if dpp dto phase is larger than modulo.

[How]
cap phase value never larger than modulo.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>