drm/i915: Replace tmds_clock_speed and link_rate with just ls_clock

drm/i915: Replace tmds_clock_speed and link_rate with just ls_clock

There's no need to distinguish between the DP link rate and HDMI TMDS
clock for the purposes of the LPE audio. Both are actually the same
thing more or less, which is the link symbol clock. So let's just
call the thing ls_clock and simplify the code.

Cc: Takashi Iwai <tiwai@suse.de>
Cc: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170427160231.13337-6-ville.syrjala@linux.intel.com
Reviewed-by: Takashi Iwai <tiwai@suse.de>