Use uniform naming for TLS 1.3 label fields

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index 53044ba..20cca31 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -35,7 +35,7 @@
     .finished     = "finished",
     .resumption   = "resumption",
     .traffic_upd  = "traffic upd",
-    .export       = "exporter",
+    .exporter     = "exporter",
     .key          = "key",
     .iv           = "iv",
     .sn           = "sn",