[XFS] Remove useless memory barrier

wake_up's implementation does an implicit memory barrier so the explicit
memory barrier is not needed in vfs_sync_worker.

Patch provided by Ralf Baechle.

SGI-PV: 960867
SGI-Modid: xfs-linux-melb:xfs-kern:28032a
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>
Signed-off-by: NDavid Chinner <dgc@sgi.com>
Signed-off-by: NTim Shimmin <tes@sgi.com>

fs/xfs/linux-2.6/xfs_super.c

@@ -553,7 +553,6 @@ vfs_sync_worker(
 		error = bhv_vfs_sync(vfsp, SYNC_FSDATA | SYNC_BDFLUSH | \
 					SYNC_ATTR | SYNC_REFCACHE, NULL);
 	vfsp->vfs_sync_seq++;
-	wmb();
 	wake_up(&vfsp->vfs_wait_single_sync_task);
 }