boards/nucleo-wl55jc: Add missing ARDUINO_I2C_UNO

The feature `arduino_i2c` was already provided, but the define this
feature indicates to be present is missing.

boards/nucleo-wl55jc/include/arduino_iomap.h

@@ -30,6 +30,16 @@
 extern "C" {
 #endif
 
+/**
+ * @name    Arduino's I2C buses
+ * @{
+ */
+/**
+ * @brief   The first I2C bus is where shields for the Arduino UNO expect it
+ */
+#define ARDUINO_I2C_UNO         I2C_DEV(0)
+/** @} */
+
 /**
  * @brief   Mapping of MCU pins to Arduino pins
  * @{