nfsd: minor off by one checks in __write_versions()
My static checker complains that if "len == remaining" then it means we
have truncated the last character off the version string.
The intent of the code is that we print as many versions as we can
without truncating a version. Then we put a newline at the end. If the
newline can't fit we return -EINVAL.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Reviewed-by: Jeff Layton <jlayton@primarydata.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>