arm: socfpga: Fix i2c mux on cyclone5-socdk board

Updated pinmux group GENERALIO[15-16] for i2c.

Signed-off-by: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Dinh Nguyen <dinh.linux@gmail.com>
Cc: Pavel Machek <pavel@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: shengjiangwu <shengjiangwu@icloud.com>