drm/i915/cnp: Ignore VBT request for know invalid DDC pin.

drm/i915/cnp: Ignore VBT request for know invalid DDC pin.

Let's ignore VBT request if the pin is clearly wrong.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104139
Cc: Kai Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180123174050.4261-1-rodrigo.vivi@intel.com
Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
(cherry picked from commit a8e6f3888b05c1e7b685800a3371ce050720368f)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>