Fix warning: print format option not compatible with size_t.

apps/s_server.c

@@ -317,7 +317,7 @@ static unsigned int psk_server_cb(SSL *ssl, const char *identity,
 		}
 	if (s_debug)
 		BIO_printf(bio_s_out,"identity_len=%d identity=%s\n",
-			identity ? strlen(identity) : 0, identity);
+			identity ? (int)strlen(identity) : 0, identity);
 
 	/* here we could lookup the given identity e.g. from a database */
   	if (strcmp(identity, psk_identity) != 0)