drm/amd/display: Correct timings in build scaling params

A previous patch set the addressable timing as active + border,
when in fact, the VESA standard specifies active as equal to
addressable + border.

This patch makes the fix more correct and in line with the standard.

Signed-off-by: Andrew Jiang <Andrew.Jiang@amd.com>
Reviewed-by: Andrew Jiang <Andrew.Jiang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>