CHROMIUM: drm: bridge/dw_hdmi: improved the hdmi audio N/CTS cacluate math

CHROMIUM: drm: bridge/dw_hdmi: improved the hdmi audio N/CTS cacluate math

The original math would bring some inaccurate to N/CTS that would
caused those magic number won't fit the HDMI 1.4 Spec request:
	128 * SampleRate = Tmds * N / CTS;

So this time we try to improved to math of N that would find the
minimal inaccurate with the HDMI 1.4 Spec.

Change-Id: Ied3cde3c352d955ae6f15d5e7fb172e92316c2a5
Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/315424
Reviewed-by: Douglas Anderson <dianders@chromium.org>