drivers: i2c_ll_stm32_v1: Generate STOP condition if NACK

Acknowledge failure (AF) error occurs when the interface detects
a NACK bit. According to the reference manual, the transmitter
which receives a NACK must reset the communication:
– If Slave: lines are released by hardware
– If Master: a Stop or repeated Start condition must be generated
  by software

Signed-off-by: Yannis Damigos <giannis.damigos@gmail.com>