@Moonshiner I'm guessing it's not working because of the DTS change.
Looks like it should be
&i2c0. See the Omega2 base DTS file for reference: https://github.com/OnionIoT/source/blob/openwrt-18.06/target/linux/ramips/dts/OMEGA2.dtsi#L142
When the firmware is running on the device, you can use
lsmod to see if the rtc kernel module is actually loaded into the kernel.