xfs: devirtualize ->sf_get_ftype and ->sf_put_ftype

Replace the ->sf_get_ftype and ->sf_put_ftype dir ops methods with
directly called xfs_dir2_sf_get_ftype and xfs_dir2_sf_put_ftype helpers
that takes care of the differences between the directory format with and
without the file type field.

Signed-off-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>