xfs: remove superflous inobt macros

xfs_ialloc_btree.h has a a cuple of macros that only obsfucate the code
but don't provide any abstraction benefits.  This patches removes those
and cleans up the reamaining defintions up a little.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
diff --git a/fs/xfs/xfs_trans_space.h b/fs/xfs/xfs_trans_space.h
index 4ea2e50..7d2c920 100644
--- a/fs/xfs/xfs_trans_space.h
+++ b/fs/xfs/xfs_trans_space.h
@@ -47,7 +47,7 @@
 #define	XFS_DIRREMOVE_SPACE_RES(mp)	\
 	XFS_DAREMOVE_SPACE_RES(mp, XFS_DATA_FORK)
 #define	XFS_IALLOC_SPACE_RES(mp)	\
-	(XFS_IALLOC_BLOCKS(mp) + XFS_IN_MAXLEVELS(mp)-1)
+	(XFS_IALLOC_BLOCKS(mp) + (mp)->m_in_maxlevels - 1)
 
 /*
  * Space reservation values for various transactions.