Use the cdclk we're going to be using when the pipe gets enabled to
compute the IPS linetime watermark. The current cdclk frequency is
irrelevant at this point since it can still change.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461940278-17122-1-git-send-email-ville.syrjala@linux.intel.comReviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>