media: cec: be smarter about detecting the number of attempts made

Some hardware does more than one attempt. So when it calls
cec_transmit_done when an error occurred it will e.g. use an error count
of 2 instead of 1.

The framework always assumed a single attempt, but now it is smarter
and will sum the counters to detect how many attempts were made.

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