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