media: pulse8-cec: queue received messages in an array

It turns out that received CEC messages can arrive faster than
can be processed by the CEC framework, resulting in lost messages.

Instead of storing only one CEC message, store up to 8.

Also fix a bug where the EOM bit wasn't checked for a received
message of length 1, so POLL messages weren't properly reported.

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