xfs: fix calculation of freed inode cluster blocks

rec.ir_startino is an agino rather than an ino.  Use the correct macro
when dealing with it in xfs_difree.
Signed-off-by: NBen Myers <bpm@sgi.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

fs/xfs/xfs_ialloc.c

@@ -1229,7 +1229,7 @@ xfs_difree(
 		}
 
 		xfs_bmap_add_free(XFS_AGB_TO_FSB(mp,
-				agno, XFS_INO_TO_AGBNO(mp,rec.ir_startino)),
+				agno, XFS_AGINO_TO_AGBNO(mp, rec.ir_startino)),
 				XFS_IALLOC_BLOCKS(mp), flist, mp);
 	} else {
 		*delete = 0;