drm/tests: cmdline: 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_cmdline_tv_options() test
never does however, which leads to a memory leak.

Let's make sure it's freed.

Reported-by: Philipp Stanner <[e-mail]>
Closes: https://lore.kernel.org/dri-devel/[e-mail]/
Fixes: e691c9992ae1 ("drm/modes: Introduce the tv_mode property as a command-line option")
Reviewed-by: Thomas Zimmermann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Maxime Ripard <[e-mail]>

drivers/gpu/drm/tests/drm_cmdline_parser_test.c

···
 #include <kunit/test.h>
 
 #include <drm/drm_connector.h>
+#include <drm/drm_kunit_helpers.h>
 #include <drm/drm_modes.h>
 
 static const struct drm_connector no_connector = {};
···
 static void drm_test_cmdline_tv_options(struct kunit *test)
 {
 	const struct drm_cmdline_tv_option_test *params = test->param_value;
-	const struct drm_display_mode *expected_mode = params->mode_fn(NULL);
+	struct drm_display_mode *expected_mode;
 	struct drm_cmdline_mode mode = { };
+	int ret;
+
+	expected_mode = params->mode_fn(NULL);
+	KUNIT_ASSERT_NOT_NULL(test, expected_mode);
+
+	ret = drm_kunit_add_mode_destroy_action(test, expected_mode);
+	KUNIT_ASSERT_EQ(test, ret, 0);
 
 	KUNIT_EXPECT_TRUE(test, drm_mode_parse_command_line_for_connector(params->cmdline,
 									  &no_connector, &mode));