Can you boot the machine?
My first thought is there was some kind of file corruption during the update, that will often either give you a 0 bit file or in rare cases, some insanely large one, but if you can boot the machine, it's not that.
The other thing you might look at is initrmfs is a cpio archive, you can list the files with a command similar to
$cpio -i -t < initrmfs
#or extract them to the local directory with
$ cpio -i -vd < initrmfs
However if the machine is operating normally, I'd just try to forget I knew how big the initrmfs was....