ui/cocoa.m: Make scrolling work again in GUI monitor windows

Make scrolling in the monitor work, by correctly passing through
control+key combinations.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Message-id: 20171101154607.1582-1-programmingkidx@gmail.com
[PMM: fixed coding style nits; cleaned up commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
1 file changed