Tweak a comment

psk_kex_mode stores the available modes - not the one which we selected.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2259)

ssl/ssl_locl.h

@@ -1114,7 +1114,7 @@ struct ssl_st {
         unsigned char *npn;
         size_t npn_len;
 
-        /* The selected PSK key exchange mode */
+        /* The available PSK key exchange modes */
         int psk_kex_mode;
     } ext;