xfs: quota limit statvfs available blocks

A "df" run on an NFS client of an exported XFS file system reports
the wrong information for "available" blocks.  When a block quota is
enforced, the amount reported as free is limited by the quota, but
the amount reported available is not (and should be).
Reported-by: NGuk-Bong, Kwon <gbkwon@gmail.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAlex Elder <aelder@sgi.com>

fs/xfs/quota/xfs_qm_bhv.c

@@ -59,7 +59,7 @@ xfs_fill_statvfs_from_dquot(
 		be64_to_cpu(dp->d_blk_hardlimit);
 	if (limit && statp->f_blocks > limit) {
 		statp->f_blocks = limit;
-		statp->f_bfree =
+		statp->f_bfree = statp->f_bavail =
 			(statp->f_blocks > be64_to_cpu(dp->d_bcount)) ?
 			 (statp->f_blocks - be64_to_cpu(dp->d_bcount)) : 0;
 	}