xfs: make use of XFS_SB_LOG_RES() at xfs_fs_log_dummy()

Make use of XFS_SB_LOG_RES() at xfs_fs_log_dummy().
Signed-off-by: NJie Liu <jeff.liu@oracle.com>
CC: Dave Chinner <david@fromorbit.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

fs/xfs/xfs_fsops.c

@@ -709,8 +709,8 @@ xfs_fs_log_dummy(
 	int		error;
 
 	tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1, KM_SLEEP);
-	error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
-					XFS_DEFAULT_LOG_COUNT);
+	error = xfs_trans_reserve(tp, 0, XFS_SB_LOG_RES(mp), 0, 0,
+				  XFS_DEFAULT_LOG_COUNT);
 	if (error) {
 		xfs_trans_cancel(tp, 0);
 		return error;