xfs: calculate XFS_TRANS_QM_QUOTAOFF space log reservation at mount time

Convert the calculation of quota off transaction log space reservation
from runtime to mount time.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
CC: Dave Chinner <david@fromorbit.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_qm_syscalls.c b/fs/xfs/xfs_qm_syscalls.c
index 1476b6f..4605f89 100644
--- a/fs/xfs/xfs_qm_syscalls.c
+++ b/fs/xfs/xfs_qm_syscalls.c
@@ -672,14 +672,10 @@
 	uint			oldsbqflag=0;
 
 	tp = xfs_trans_alloc(mp, XFS_TRANS_QM_QUOTAOFF);
-	if ((error = xfs_trans_reserve(tp, 0,
-				      sizeof(xfs_qoff_logitem_t) * 2 +
-				      mp->m_sb.sb_sectsize + 128,
-				      0,
-				      0,
-				      XFS_DEFAULT_LOG_COUNT))) {
+	error = xfs_trans_reserve(tp, 0, XFS_QM_QUOTAOFF_LOG_RES(mp),
+				  0, 0, XFS_DEFAULT_LOG_COUNT);
+	if (error)
 		goto error0;
-	}
 
 	qoffi = xfs_trans_get_qoff_item(tp, NULL, flags & XFS_ALL_QUOTA_ACCT);
 	xfs_trans_log_quotaoff_item(tp, qoffi);