Acabei de remover o arquivo /usr/share/doc/libdrm2/changelog.Debian.gz
e a atualização funcionou sem problemas.
....
Setting up libdrm2:amd64 (2.4.39-0ubuntu1) ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
Processing triggers for initramfs-tools ...
update-initramfs: Generating /boot/initrd.img-3.5.0-18-generic