drm/i915/audio: drop extra crtc clock check from HDMI audio N lookup

The array contains the crtc clock, rely on that. While at it, debug log
the HDMI N value or automatic mode.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: "Lin, Mengdong" <mengdong.lin@intel.com>
Cc: Libin Yang <libin.yang@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477407258-30599-2-git-send-email-jani.nikula@intel.com