media: cec-ioc-adap-g-caps.rst: document available_log_addrs

The CEC_ADAP_G_CAPS documentation of the cec_caps struct was missing
the available_log_addrs field. Add this.

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