lafs_iget takes a filesystem-inode rather than a super_block.

lafs_iget takes a filesystem-inode rather than a super_block.

On the path to reducing the number of superblocks.... each superblock
can hold multiple subset filesystems so we need more than the
inode number to identify a file - we need the filesystem inode too.

So change lafs_iget to take a filesystem inode rather than a
superblock.

We still need to get at the superblock.  In a few patches we can just
use ->i_sb, but for now it might not be the same so stash it in
i_private.

Signed-off-by: NeilBrown <neilb@suse.de>