Add return value check for cerificate verify

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 45692d8..75b11c9 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -503,6 +503,7 @@
 cleanup:
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate verify" ) );
+    MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_tls13_process_certificate_verify", ret );
     return( ret );
 #else
     ((void) ssl);