drm/amd/display: Fixed comment styling

Switched to C-style comments for consistency

Signed-off-by: Haiyi Zhou <haiyi.zhou@amd.com>
Reviewed-by: Reza Amini <Reza.Amini@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>