NFS: Revert commit 44dd151d

Revert commit 44dd151d "NFS: Don't mark a written page as uptodate until it
is on disk". While it is true that the write may fail, that is always the
case. There is no reason why we should treat data on pages that are not
already marked as PG_uptodate as being special. The only thing we gain is a
noticeable slowdown when re-reading these pages.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>