xfs: fixes for 3.15-rc6

Code inspection of the XFS error number sign translations found a bunch of
issues, including returning incorrectly signed errors for some data integrity
operations. These leak to userspace and result in applications not getting the
errors correctly reported. Hence they need fixing sooner rather than later.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
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=5syB
-----END PGP SIGNATURE-----