drm/edid: Add a FIXME about DispID CEA data block revision

drm/edid: Add a FIXME about DispID CEA data block revision

I don't understand what the DispID CEA data block revision
means. The spec doesn't say. I guess some DispID must have
a value of >= 3 in there or else we generally wouldn't
even parse the CEA data blocks. Or does all this code
actually not do anything?

Cc: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200124200231.10517-6-ville.syrjala@linux.intel.com
Reviewed-by: Andres Rodriguez <andresx7@gmail.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>