media: pulse8-cec: use adap_free callback

Don't free everything in the disconnect callback, instead use
the adap_free callback, which is called when the last open
filehandle is closed.

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