Fix return values for TLS 1.3 state machine code.

This is a no-op because all affected codepaths are either unreachable or
are fine because ssl_hs_error (intentionally, since C doesn't help us
any) aligns with zero. Still, fix these.

Change-Id: Ieba4e3eec3881a56b5ddcd32abdd2c9dda875eda
Reviewed-on: https://boringssl-review.googlesource.com/12313
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Steven Valdez <svaldez@chromium.org>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
diff --git a/ssl/tls13_client.c b/ssl/tls13_client.c
index ebe7703..ee82535 100644
--- a/ssl/tls13_client.c
+++ b/ssl/tls13_client.c
@@ -421,7 +421,7 @@
   if (!tls13_check_message_type(ssl, SSL3_MT_CERTIFICATE_VERIFY) ||
       !tls13_process_certificate_verify(ssl) ||
       !ssl_hash_current_message(ssl)) {
-    return 0;
+    return ssl_hs_error;
   }
 
   hs->state = state_process_server_finished;