drm/i915: Fix the old vs. new epoch counter check during hotplug detect

The old epoch counter was left uninited, so the function returned a
changed state always.

While at it debug print the old epoch counter as well.

Fixes: 35205ee9 ("drm/i915: Send hotplug event if edid had changed")
Cc: Kunal Joshi <kunal1.joshi@intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200701180001.15857-1-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_hotplug.c

@@ -279,6 +279,7 @@ intel_encoder_hotplug(struct intel_encoder *encoder,
 
 	drm_WARN_ON(dev, !mutex_is_locked(&dev->mode_config.mutex));
 	old_status = connector->base.status;
+	old_epoch_counter = connector->base.epoch_counter;
 
 	connector->base.status =
 		drm_helper_probe_detect(&connector->base, NULL, false);
@@ -287,11 +288,12 @@ intel_encoder_hotplug(struct intel_encoder *encoder,
 		ret = true;
 
 	if (ret) {
-		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s(epoch counter %llu)\n",
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s (epoch counter %llu->%llu)\n",
 			      connector->base.base.id,
 			      connector->base.name,
 			      drm_get_connector_status_name(old_status),
 			      drm_get_connector_status_name(connector->base.status),
+			      old_epoch_counter,
 			      connector->base.epoch_counter);
 		return INTEL_HOTPLUG_CHANGED;
 	}