[XFS] Fix regression in xfs_buf_rele dealing with non-hashed buffers, as

occur during log replay.  Novell bug 145204, Fedora bug 177848.

SGI-PV: 948860
SGI-Modid: xfs-linux-melb:xfs-kern:25064a

Signed-off-by: Nathan Scott <nathans@sgi.com>