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.comReviewed-by: Andres Rodriguez <andresx7@gmail.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>

drivers/gpu/drm/drm_edid.c

@@ -3993,6 +3993,13 @@ cea_db_tag(const u8 *db)
 static int
 cea_revision(const u8 *cea)
 {
+	/*
+	 * FIXME is this correct for the DispID variant?
+	 * The DispID spec doesn't really specify whether
+	 * this is the revision of the CEA extension or
+	 * the DispID CEA data block. And the only value
+	 * given as an example is 0.
+	 */
 	return cea[1];
 }