xfs: truncate transaction does not modify the inobt

xfs: truncate transaction does not modify the inobt

Source kernel commit: a606ebdb859e78beb757dfefa08001df366e2ef5

The truncate transaction does not ever modify the inode btree, but
includes an associated log reservation. Update
xfs_calc_itruncate_reservation() to remove the reservation
associated with inobt updates.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>