NFS: add an endian notation for sparse

This is supposed to be a __be32 value.  Sparse complains a lot:

fs/nfs/callback_xdr.c:699:30: warning: incorrect type in initializer (different base types)
fs/nfs/callback_xdr.c:699:30:    expected unsigned int [unsigned] status
fs/nfs/callback_xdr.c:699:30:    got restricted __be32 const [usertype] csr_status
fs/nfs/callback_xdr.c:715:9: warning: cast to restricted __be32
fs/nfs/callback_xdr.c:716:16: warning: incorrect type in return expression (different base types)
fs/nfs/callback_xdr.c:716:16:    expected restricted __be32
fs/nfs/callback_xdr.c:716:16:    got unsigned int [unsigned] status

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>