[m-rev.] for post commit review: fix unintelligible compiler message

[Zoltan Somogyi]

On Wed, 13 Mar 2019 16:01:53 +1100, Peter Wang <novalazy at gmail.com> wrote:
> > +    ( if NumExtra > 0 then
> > +        % The callee's argument list contains extra typeinfo and/or
> > +        % typeclass_info arguments added by polymorphism.m. Usually,
> > +        % these extra arguments are all already ground, which means that
> > +        % they cannot be insufficiently instantiated. And since users cannot
> > +        % require them to have any inst more specific than ground, they
> > +        % cannot be the cause of any mode errors. This is why we do not
> > +        % report their instantations.
> 
> instantiations

Fixed. Thanks for the review.

Zoltan.