xfs: use unsigned int for all size values in struct xfs_da_geometry

None of these can ever be negative, so use unsigned types.

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>