ieee1394: pcilynx: I2C cleanups

* Delete optional and empty i2c client_register and client_unregister
  callbacks.
* Use the proper i2c adapter ID.
* Don't use a template to initialize the i2c_adapter structure, it's
  inefficient.
* Update a misleading comment on why we use i2c_transfer rather than
  higher level i2c functions.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>