V4L/DVB (11423): gspca - m5602-ov9650: Add a disconnect hook, setup a ctrl cache ctrl.

Reading and writing to a register doesn't always work reliably. Add a cache
and ensure that it is deallocated properly upon module disconnect.

Signed-off-by: Erik Andr?n <erik.andren@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>