Only return VERIFY_FAILED from a single point

Everything else is a fatal error. Also improve documentation about that for
the vrfy callback.
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index 6df5298..ea56f3f 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -1204,7 +1204,7 @@
 
 X509 CRT verify long chain (max intermediate CA + 1)
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
-mbedtls_x509_crt_verify_max:"data_files/dir-maxpath/00.crt":"data_files/dir-maxpath":MBEDTLS_X509_MAX_INTERMEDIATE_CA+1:MBEDTLS_ERR_X509_CERT_VERIFY_FAILED:-1
+mbedtls_x509_crt_verify_max:"data_files/dir-maxpath/00.crt":"data_files/dir-maxpath":MBEDTLS_X509_MAX_INTERMEDIATE_CA+1:MBEDTLS_ERR_X509_FATAL_ERROR:-1
 
 X509 CRT verify chain #1 (zero pathlen intermediate)
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_RSA_C