The straightforward solution would be to run file overwriting process by sending the following command:
sudo dpkg -i --force-all /var/cache/apt/archives/linux-firmware-raspi2_1.20190215-0ubuntu0.18.04.1_armhf.deb
and then resume the upgrade process with
sudo apt-get upgrade
Update: previously I have a typo here --force --all instead of --force-all.