NFSD: Correct type annotations in user xattr XDR functions

Squelch some sparse warnings:

/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4692:24: warning: incorrect type in return expression (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4692:24:    expected int
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4692:24:    got restricted __be32 [usertype]
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4702:32: warning: incorrect type in return expression (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4702:32:    expected int
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4702:32:    got restricted __be32 [usertype]
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4739:13: warning: incorrect type in assignment (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4739:13:    expected restricted __be32 [usertype] err
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4739:13:    got int
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4891:15: warning: incorrect type in assignment (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4891:15:    expected unsigned int [assigned] [usertype] count
/home/cel/src/linux/linux/fs/nfsd/nfs4xdr.c:4891:15:    got restricted __be32 [usertype]

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