media: cec: use call_op and check for !unregistered

Use call_(void_)op consistently in the CEC core framework. Ditto
for the cec pin ops. And check if !adap->devnode.unregistered before
calling each op. This avoids calls to ops when the device has been
unregistered and the underlying hardware may be gone.

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