greybus: hotplug function doesn't need to contain manifest now

Manifest is fetched with control protocol now and so we don't need space
for it in hotplug data.

Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>