drm/i915: Fix SKL DDI A digital port .connected()

SKL doesn't have any north DE hotplug stuff. Currently we're
trying to read DDI A live state from the BDW north DE bit,
instead of the approproate south DE bit. Fix it.

And for good measure clear the pointer to the north hpd
pin array, so that we'll actually notice if some other
place is also using the wrong thing.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230302161013.29213-3-ville.syrjala@linux.intel.com