drm/edid: no CEA v3 extension is not an error

It is fine for displays without audio functionality to not implement
CEA v3 extension in their EDID. Do not return an error in that case,
instead return 0 as if there was a CEA v3 extension with no audio or
speaker block.

This fixes the second half of bug fdo#107825:
https://bugs.freedesktop.org/show_bug.cgi?id=107825Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191115170736.7d88593d@endymion

drivers/gpu/drm/drm_edid.c

@@ -4279,12 +4279,12 @@ int drm_edid_to_sad(struct edid *edid, struct cea_sad **sads)
 	cea = drm_find_cea_extension(edid);
 	if (!cea) {
 		DRM_DEBUG_KMS("SAD: no CEA Extension found\n");
-		return -ENOENT;
+		return 0;
 	}
 
 	if (cea_revision(cea) < 3) {
 		DRM_DEBUG_KMS("SAD: wrong CEA revision\n");
-		return -EOPNOTSUPP;
+		return 0;
 	}
 
 	if (cea_db_offsets(cea, &start, &end)) {
@@ -4340,12 +4340,12 @@ int drm_edid_to_speaker_allocation(struct edid *edid, u8 **sadb)
 	cea = drm_find_cea_extension(edid);
 	if (!cea) {
 		DRM_DEBUG_KMS("SAD: no CEA Extension found\n");
-		return -ENOENT;
+		return 0;
 	}
 
 	if (cea_revision(cea) < 3) {
 		DRM_DEBUG_KMS("SAD: wrong CEA revision\n");
-		return -EOPNOTSUPP;
+		return 0;
 	}
 
 	if (cea_db_offsets(cea, &start, &end)) {