boards: disco_l475_iot1: fix arduino_i2c assignment

0f05f58bf5 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 a2da571172)

boards/st/disco_l475_iot1/arduino_r3_connector.dtsi

@@ -35,6 +35,6 @@
 	};
 };
 
-arduino_i2c: &i2c3 {};
+arduino_i2c: &i2c1 {};
 arduino_spi: &spi1 {};
 arduino_serial: &uart4 {};