v1.8.3

This release updates FatFS (the FAT filesystem library) to the latest patch
release, R0.14a.

It also updates how fwup calls into the library to reduce the time window where
fwup can be responsible for FAT filesystem corruption. The incident that
prompted this change was a device that had repeated firmware update
interruptions had accumulated enough orphaned FAT clusters to fill the partition
and prevent an update. fsck.fat can fix this easily, but it's better if this
doesn't happen and this update should reduce the probability.