afs: Use cell for md5 inode numbers

afs: Use cell for md5 inode numbers

When calculating the inode number for a file with md5 inodes, include
the cell number in the calculation, in order to reduce collisions
between cells.

Change-Id: I4b939042dd993419f785a78e87e68cf346b56e26
Reviewed-on: http://gerrit.openafs.org/4902
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>