[media] pulse8-cec: serialize communication with adapter

Make sending messages to the adapter serialized within the driver.

send_and_wait is split into send_and_wait_once, which only sends once
and checks for the result, and the higher level send_and_wait, which
performs locking and retries.

Signed-off-by: Johan Fjeldtvedt <jaffe1@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>