xfs: fix inode allocation block res calculation precedence

The block reservation calculation for inode allocation is supposed
to consist of the blocks required for the inode chunk plus
(maxlevels-1) of the inode btree multiplied by the number of inode
btrees in the fs (2 when finobt is enabled, 1 otherwise).

Instead, the macro returns (ialloc_blocks + 2) due to a precedence
error in the calculation logic. This leads to block reservation
overruns via generic/531 on small block filesystems with finobt
enabled. Add braces to fix the calculation and reserve the
appropriate number of blocks.

Fixes: 9d43b180 ("xfs: update inode allocation/free transaction reservations for finobt")
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_trans_space.h

@@ -57,7 +57,7 @@
 	XFS_DAREMOVE_SPACE_RES(mp, XFS_DATA_FORK)
 #define	XFS_IALLOC_SPACE_RES(mp)	\
 	(M_IGEO(mp)->ialloc_blks + \
-	 (xfs_sb_version_hasfinobt(&mp->m_sb) ? 2 : 1 * \
+	 ((xfs_sb_version_hasfinobt(&mp->m_sb) ? 2 : 1) * \
 	  (M_IGEO(mp)->inobt_maxlevels - 1)))
 
 /*