Fix qemu_event_init

Falling through to "fail" made qemu_event_init() close the pipe fds
immediately again, breaking timer event notification.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

vl.c

@@ -3713,6 +3713,8 @@ static int qemu_event_init(void)
                          (void *)(unsigned long)fds[0]);
 
     io_thread_fd = fds[1];
+    return 0;
+
 fail:
     close(fds[0]);
     close(fds[1]);