docs: i2c: i2c-protocol: use same wording as smbus-protocol

In smbus-protocol.rst we use the text "Implemented by" for the same meaning
as "This corresponds to". Change everything to "Implemented by" for
coherency.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reported-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>