drm/amd/display: pass vline_config parameter by reference.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>