drm/i915/audio: use the same code for updating audio config

It gets fragile to duplicate the code for updating HSW_AUD_CFG. The only
change should be that the hdmi pixel clock is also updated in
i915_audio_component_sync_audio_rate(), but it should not be any
different.

Cc: Libin Yang <libin.yang@linux.intel.com>
Reviewed-by: Libin Yang <libin.yang@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/e0e88ec00c0ed1734083153b55283efd3116be5c.1476111629.git.jani.nikula@intel.com