Driver: i2c_ll_stm32_v2: Remove log msg on boot

Converts the `<inf> i2c_ll_stm32_v2: I2C TIMING` message
displayed by the driver to a LOG_DBG. Also makes an actual
error message a LOG_ERR instead of a LOG_DBG.

Signed-off-by: Glenn Andrews <glenn.andrews.42@gmail.com>