xfs: merge the projid fields in struct xfs_icdinode

There is no point in splitting the fields like this in an purely
in-memory structure.

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>