drm/amd/display: Do not access fbdev helper members

Original code is no longer needed and tested without loop.

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