drivers: i2c: i2c-priv: drop logging

i2c_map_dt_bitrate uses LOG_ERR, however, one must define (or declare) a
log module where to sink the logs. Since this sits on a header file,
it creates a hidden include order dependency: you must include
i2c-priv.h after registering or declaring a log module on your driver.
Even worse, you are force to use logging in your drivers even if you do
not want to!

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>