If you can ssh to Pi, you can go to the folder where the firmware is installed (generally your home folder OpenSprinkler-Firmware subfolder), then rename nvm.dat to something else, like nvm.bak, then reboot Pi. This will basically trigger a firmware reset and it will recover the port number of 8080.
The renamed nvm.dat has all your configurations preserved and there is a way to use a binary file editor to directly edit that file to change the port to something else.