[media] cec: improve debug messages

- use __func__ instead of writing the full function name
- drop debug message in cec_config_log_addr since the same information
  will be reported later
- use debug level 1 for errors and infrequent events, use level 2 for
  debugging CEC message traffic
- log when a transmit is retried, very useful to know when debugging
- debug messages now all start with lower case

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