drm/amd/display: Fixed non-native modes not lighting up

There is no need to call drm_mode_set_crtcinfo() again once
crtc timing is decided. Otherwise non-native/unsupported timing
might get overwritten.

Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>