It's common to share screens within CI labs, and it's also common for
KVM switches to alter the contents of the CEA block but leave the
checksum outdated.

So in this case, print a debug message instead of an error.

References: https://bugs.freedesktop.org/show_bug.cgi?id=98228
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Tested-by: Jari Tahvanainen <jari.tahvanainen@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1481202716-31317-1-git-send-email-tomeu.vizoso@collabora.com