drm/i915: Fix CD2X pipe select masking during cdclk sanitation

We're forgetting to mask off all three pipe select bits from the
CDCLK_CTL value on icl+ which may lead to the extra bit being
left in. That will cause us to consider the current hardware
cdclk state as invalid, and we proceed to sanitize it even
though the hardware may have active pipes and whatnot.

Fix up the mask so we get rid of all three pipe select bits
and thus hopefully no longer sanitize cdclk when it's already
correctly programmed.

Cc: Matt Roper <matthew.d.roper@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111641


Fixes: 0c1279b5 ("drm/i915: Consolidate {bxt,cnl,icl}_init_cdclk")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190911133129.27466-2-ville.syrjala@linux.intel.com