xfs: calculate XFS_TRANS_QM_QUOTAOFF_END space log reservation at mount time

Convert the calculation for end of quotaoff 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 4605f89..cf9a340 100644
--- a/fs/xfs/xfs_qm_syscalls.c
+++ b/fs/xfs/xfs_qm_syscalls.c
@@ -639,8 +639,9 @@
 
 	tp = xfs_trans_alloc(mp, XFS_TRANS_QM_QUOTAOFF_END);
 
-	if ((error = xfs_trans_reserve(tp, 0, sizeof(xfs_qoff_logitem_t) * 2,
-				      0, 0, XFS_DEFAULT_LOG_COUNT))) {
+	error = xfs_trans_reserve(tp, 0, XFS_QM_QUOTAOFF_END_LOG_RES(mp),
+				  0, 0, XFS_DEFAULT_LOG_COUNT);
+	if (error) {
 		xfs_trans_cancel(tp, 0);
 		return (error);
 	}