boards/stm32f4discovery: Change sda pin
boards/stm32f4discovery: Change sda pin

This commit changes the I2C0 SDA pin to 9 from 7.
This is because the CS43L22 is connected to scl6 and sda9.

ant9000/RIOT,miri64/RIOT,kaspar030/RIOT,jasonatran/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,ant9000/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,miri64/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,miri64/RIOT,authmillenon/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kaspar030/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,OTAkeys/RIOT,authmillenon/RIOT,jasonatran/RIOT,miri64/RIOT,OTAkeys/RIOT,miri64/RIOT,authmillenon/RIOT,ant9000/RIOT,OTAkeys/RIOT,jasonatran/RIOT,authmillenon/RIOT,authmillenon/RIOT,kYc0o/RIOT