Revert "drm/i915/dp: Zero the DPCD data before connection probe"

This reverts commit 97cdd71010.

Clearing the dpcd data means that if the fetch fails, any previous
data will be lost. On eDP, this is no fun as we only fetch dpcd at
init time, so the memset will destroy that the next time through.

drivers/gpu/drm/i915/intel_dp.c

@@ -1697,7 +1697,6 @@ intel_dp_detect(struct drm_connector *connector, bool force)
 	struct edid *edid = NULL;
 
 	intel_dp->has_audio = false;
-	memset(intel_dp->dpcd, 0, sizeof(intel_dp->dpcd));
 
 	if (HAS_PCH_SPLIT(dev))
 		status = ironlake_dp_detect(intel_dp);