xfs: remove unnecessary dfops init calls in xattr code

Each xfs_defer_init() call in the xattr code uses the internal dfops
reference. In addition, a successful xfs_defer_finish() always
returns with a reset xfs_defer_ops structure.

Given that along with the fact that every xfs_defer_init() call in
the xattr code is followed up by an xfs_defer_finish(), the former
calls are no longer necessary and can be removed.

Note that the xfs_defer_init() call in the remote value copy loop of
xfs_attr_rmtval_set() is not followed by a finish, but the dfops is
unused in this instance.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Bill O'Donnell <billodo@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>