drm/tests: client: Mention that we can't use MODULE_ macros

That file is included directly, so we can't use any MODULE macro. Let's
leave a comment to avoid any future mistake.
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
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-v10-1-256dad125326@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/tests/drm_client_modeset_test.c

@@ -96,3 +96,8 @@ static struct kunit_suite drm_test_pick_cmdline_test_suite = {
 };
 
 kunit_test_suite(drm_test_pick_cmdline_test_suite);
+
+/*
+ * This file is included directly by drm_client_modeset.c so we can't
+ * use any MODULE_* macro here.
+ */