Drop superfluous parenthesis around VMPortReadFunc typedef
(added in d67f679d, missed to remove when moved in e5951129).

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200505142836.16903-1-philmd@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>