drm/edid: shorten log output in case of all zeroes edid block

There is no need to dump the whole EDID block in case it contains no
information. Just print a single line stating the block is empty instead
of 8 lines containing only zeroes.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>