[media] cx23885: uninitialized variable in cx23885_av_work_handler()

The "handled" variable could be uninitialized if the
interrupt_service_routine() call back hasn't been implimented or if it
has been implemented but doesn't initialize "handled" to zero at the
start.  For example, adv76xx_isr() only sets "handled" to true.

Fixes: 44b153ca ('[media] m5mols: Add ISO sensitivity controls')

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>