media: vivid: call v4l2_event_wake_all() on disconnect

When the disconnect error injection control is set, then besides
faking unregistering the device nodes, also call v4l2_event_wake_all()
to ensure any userspace applications will wake up as per a 'normal'
unregister.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>