drm/tests: probe-helper: Fix drm_display_mode memory leak

drm_analog_tv_mode() and its variants return a drm_display_mode that
needs to be destroyed later one. The
drm_test_connector_helper_tv_get_modes_check() test never does however,
which leads to a memory leak.

Let's make sure it's freed.

Reported-by: Philipp Stanner <phasta@mailbox.org>
Closes: https://lore.kernel.org/dri-devel/a7655158a6367ac46194d57f4b7433ef0772a73e.camel@mailbox.org/
Fixes: 1e4a91d ("drm/probe-helper: Provide a TV get_modes helper")
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250408-drm-kunit-drm-display-mode-memleak-v1-7-996305a2e75a@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

Author: mripard

drivers/gpu/drm/tests/drm_probe_helper_test.c

@@ -98,7 +98,7 @@ drm_test_connector_helper_tv_get_modes_check(struct kunit *test)
 	struct drm_connector *connector = &priv->connector;
 	struct drm_cmdline_mode *cmdline = &connector->cmdline_mode;
 	struct drm_display_mode *mode;
-	const struct drm_display_mode *expected;
+	struct drm_display_mode *expected;
 	size_t len;
 	int ret;
 
@@ -134,6 +134,9 @@ drm_test_connector_helper_tv_get_modes_check(struct kunit *test)
 
 		KUNIT_EXPECT_TRUE(test, drm_mode_equal(mode, expected));
 		KUNIT_EXPECT_TRUE(test, mode->type & DRM_MODE_TYPE_PREFERRED);
+
+		ret = drm_kunit_add_mode_destroy_action(test, expected);
+		KUNIT_ASSERT_EQ(test, ret, 0);
 	}
 
 	if (params->num_expected_modes >= 2) {
@@ -145,6 +148,9 @@ drm_test_connector_helper_tv_get_modes_check(struct kunit *test)
 
 		KUNIT_EXPECT_TRUE(test, drm_mode_equal(mode, expected));
 		KUNIT_EXPECT_FALSE(test, mode->type & DRM_MODE_TYPE_PREFERRED);
+
+		ret = drm_kunit_add_mode_destroy_action(test, expected);
+		KUNIT_ASSERT_EQ(test, ret, 0);
 	}
 
 	mutex_unlock(&priv->drm->mode_config.mutex);