Revert "drm/i915: shut up gen8+ SDE irq dmesg noise"

This reverts

commit 97e5ed11
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Oct 23 10:56:12 2015 +0200

    drm/i915: shut up gen8+ SDE irq dmesg noise

With the proper fix ("drm/i915: fix the SDE irq dmesg warnings
properly") reliably in place, bring back the error message.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448462843-32739-2-git-send-email-jani.nikula@intel.com