explicitly use c->fd instead of fd

Yep, fd should be the file descriptor, but for lazyness when manually
calling the function sometimes we supply 0 as fd and event.  Instead of
fixing the usage, do as other of such functions do in this
circumstances: use c->fd.

server.c

@@ -1109,10 +1109,10 @@ close_conn(int fd, short ev, void *d)
 
 	switch (tls_close(c->ctx)) {
 	case TLS_WANT_POLLIN:
-		yield_read(fd, c, &close_conn);
+		yield_read(c->fd, c, &close_conn);
 		return;
 	case TLS_WANT_POLLOUT:
-		yield_read(fd, c, &close_conn);
+		yield_read(c->fd, c, &close_conn);
 		return;
 	}