xfs: improve xfs_inobt_update prototype

Both callers of xfs_inobt_update have the record in form of a
xfs_inobt_rec_incore_t, so just pass a pointer to it instead of the
individual variables.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Felix Blyakher <felixb@sgi.com>