NFS: Clean up nfs read and write error paths

Move the error handling for nfs_generic_pagein() into a single function.
Ditto for nfs_generic_flush().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Fred Isaman <iisaman@netapp.com>

diff --cc fs/nfs/pnfs.c
Simple merge

diff --cc fs/nfs/read.c
Simple merge

diff --cc fs/nfs/write.c
Simple merge