NFSD: Correct type annotations in COPY XDR functions

Squelch some sparse warnings:

/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:1860:16: warning: incorrect type in assignment (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:1860:16:    expected int status
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:1860:16:    got restricted __be32
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:1862:24: warning: incorrect type in return expression (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:1862:24:    expected restricted __be32
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:1862:24:    got int status

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>