drm/tests: probe_helper: Fix uninitialized variable

The len variable is used while uninitialized. Initialize it.

Fixes: 1e4a91db ("drm/probe-helper: Provide a TV get_modes helper")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20221201090736.290935-1-maxime@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/tests/drm_probe_helper_test.c

@@ -115,6 +115,7 @@ drm_test_connector_helper_tv_get_modes_check(struct kunit *test)
 	ret = drm_connector_helper_tv_get_modes(connector);
 	KUNIT_EXPECT_EQ(test, ret, params->num_expected_modes);
 
+	len = 0;
 	list_for_each_entry(mode, &connector->probed_modes, head)
 		len++;
 	KUNIT_EXPECT_EQ(test, len, params->num_expected_modes);