Change slave address in I2C master slave asynch test

Change test slave address to 0x80 because 0x90 is used by a real slave
(temperature sensor) on few boards like the CI shield.

Author: LMESTM

features/unsupported/tests/mbed/i2c_master_slave_asynch/main.cpp

@@ -14,7 +14,7 @@
   #error [NOT_SUPPORTED] I2C Async is not supported
 #endif
 
-#define ADDR (0x90)
+#define ADDR (0x80)
 #define FREQ 100000
 #define SIZE 10