MicroBit.I2C: clean up device definition
MicroBit.I2C: clean up device definition

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