drm/radeon/audio: improve ACR calculation

commit a2098250fbda149cfad9e626afe80abe3b21e574 upstream.

In order to have any realistic chance of calculating proper
ACR values, we need to be able to calculate both N and CTS,
not just CTS. We still aim for the ideal N as specified in
the HDMI spec though.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=69675



Signed-off-by: Pierre Ossman <pierre@ossman.eu>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>