xfs: rename struct xfs_attr_item to xfs_attr_intent

Everywhere else in XFS, structures that capture the state of an ongoing
deferred work item all have names that end with "_intent".  The new
extended attribute deferred work items are not named as such, so fix it
to follow the naming convention used elsewhere.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>