NFSv4: Clean up nfs4_open_revalidate

Remove references to 'struct nameidata' from the low-level open_revalidate
code, and replace them with a struct nfs_open_context which will be
correctly initialised upon success.

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

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

diff --cc fs/nfs/nfs4_fs.h
Simple merge

diff --cc fs/nfs/nfs4proc.c
Simple merge