A while back, the read_inode method was removed in favor of implementing
jfs_iget rather than just iget.  However, since JFS does not implement it's
own get_dentry export_operation, the generic iget can still be called.
Therefore, we do need the read_inode method, so switch back to defining
jfs_read_inode, and use iget rather than jfs_iget.

This fixes bugzilla.kernel.org's bug #796.