You don’t need to have package ntpd, which you have installed as it is provided by busybox.
What you need to do is to remove package ntpd, which you have installed and run pkgupdate again.
Also, it is not possible to install it. See following error:
Collected errors:
* check_data_file_clashes: Package ntpd wants to install file /sbin/ntpd
But that file is already provided by package * busybox
* opkg_install_cmd: Cannot install package ntpd.