libxfs: error negation rework

libxfs: error negation rework

The libxfs core in the kernel now returns negative error numbers one
failure rather than positive numbers. This commit switches the
libxfs core to use negative error numbers and converts all
the libxfs function callers to negate the returned error so that
none of the other codeneeds tobe changed at this time.

This allows us to drive negative errors through the xfsprogs code
base at our leisure rather than having to do it all right now.

Signed-off-by: Dave Chinner <dchinner@redhat.com>