drivers: i2c_ll_stm32: Fix building for interrupt mode

The compilation of the i2c_ll_stm32 fails when we
enable the interrupt mode. The struct i2c_stm32_data
is needed to initialize the semaphore. This patch adds
the missing struct for interrupt mode.

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