[XFS] handle unaligned data in xfs_bmbt_disk_get_all

In libxfs xfs_bmbt_disk_get_all needs to handle unaligned data and thus
has been updated to use get_unaligned_be64.  In kernelspace we don't strictly
need it as the routine is only used for tracing and xfsidbg, but let's keep
the two implementations in sync.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>