boards: disco_l475_iot1: fix arduino_i2c assignment

https://github.com/zephyrproject-rtos/zephyr/commit/0f05f58bf51b1fa74413cac4522306321a1ecd2e

 assigned the `arduino_i2c` to the incorrect pins for the Arduino UNO connector. This assigns them back.

signed-off-by: Glenn Andrews <glenn.andrews.42@gmail.com>
(cherry picked from commit a2da5711)