[XFS] Fix nused counter. It's currently getting set to -1 rather than

getting decremented by 1.  Since nused never reaches 0, the "if
(!free->hdr.nused)" check in xfs_dir2_leafn_remove() fails every time and
xfs_dir2_shrink_inode() doesn't get called when it should.  This causes
extra blocks to be left on an empty directory and the directory in unable
to be converted back to inline extent mode.

SGI-PV: 951958
SGI-Modid: xfs-linux-melb:xfs-kern:211382a
Signed-off-by: NMandy Kirkconnell <alkirkco@sgi.com>
Signed-off-by: NNathan Scott <nathans@sgi.com>

fs/xfs/xfs_dir2_node.c

@@ -972,7 +972,7 @@ xfs_dir2_leafn_remove(
 			/*
 			 * One less used entry in the free table.
 			 */
-			free->hdr.nused = cpu_to_be32(-1);
+			be32_add(&free->hdr.nused, -1);
 			xfs_dir2_free_log_header(tp, fbp);
 			/*
 			 * If this was the last entry in the table, we can