STM32F4.I2C: Fix flag name
STM32F4.I2C: Fix flag name

ellamosi/Ada_BMP_Library,simonjwright/Ada_Drivers_Library,Fabien-Chouteau/Ada_Drivers_Library,Fabien-Chouteau/Ada_Drivers_Library,AdaCore/Ada_Drivers_Library,AdaCore/Ada_Drivers_Library,simonjwright/Ada_Drivers_Library