drm/radeon: fix N/CTS clock matching for audio

The drm code that calculates the 1001 clocks rounds up
rather than truncating.  This allows the table to match
properly on those modes.

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



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>