drm/i915/audio: extend audio sync rate support for DP MST

Remove the type judgement in i915_audio_component_sync_audio_rate().
Audio rate sync is necessary for all i915 digital audio now.

Signed-off-by: Libin Yang <libin.yang@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480569439-54252-2-git-send-email-libin.yang@intel.com