drm/connector: Only register TV mode property if present

The drm_create_tv_properties() will create the TV mode property
unconditionally.

However, since we'll gradually phase it out, let's register it only if we
have a list passed as an argument. This will make the transition easier.
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Acked-in-principle-or-something-like-that-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v10-3-256dad125326@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/drm_connector.c

@@ -1690,15 +1690,18 @@ int drm_mode_create_tv_properties(struct drm_device *dev,
 	if (drm_mode_create_tv_margin_properties(dev))
 		goto nomem;
 
-	dev->mode_config.legacy_tv_mode_property =
-		drm_property_create(dev, DRM_MODE_PROP_ENUM,
-				    "mode", num_modes);
-	if (!dev->mode_config.legacy_tv_mode_property)
-		goto nomem;
 
-	for (i = 0; i < num_modes; i++)
-		drm_property_add_enum(dev->mode_config.legacy_tv_mode_property,
-				      i, modes[i]);
+	if (num_modes) {
+		dev->mode_config.legacy_tv_mode_property =
+			drm_property_create(dev, DRM_MODE_PROP_ENUM,
+					    "mode", num_modes);
+		if (!dev->mode_config.legacy_tv_mode_property)
+			goto nomem;
+
+		for (i = 0; i < num_modes; i++)
+			drm_property_add_enum(dev->mode_config.legacy_tv_mode_property,
+					      i, modes[i]);
+	}
 
 	dev->mode_config.tv_brightness_property =
 		drm_property_create_range(dev, 0, "brightness", 0, 100);