media: cec-core.rst/cec-ioc-g-mode.rst: fix typos in monitor-all description

cec-core.rst was missing 'are', and cec-ioc-g-mode.rst was missing
a comma.

In both cases this made the description of the Monitor All functionality
hard to read.

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