AmebaZ - update OTA2 address upon flashing

[kuba2k2]

This is very annoying, especially on Realtek boards. Flashing UF2 writes it to OTA2, and if the address is mismatched (e.g. by compiling for a wrong board - with a different OTA2 partition address), the bootloader boots OTA1 again. And then I spend countless hours trying to figure out why the program doesn't work, before realizing that the changes were never actually booted.