NFS: "const static" vs "static const" in nfs4

My previous "const static" vs "static const" cleanup missed a single case,
patch below takes care of it.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>