examples/hwapi: Use Signal for inverted LED on ESP-12.

examples/hwapi/hwconfig_esp8266_esp12.py

-from machine import Pin
+from machine import Pin, Signal
 
 # ESP12 module as used by many boards
-# Blue LED on pin 2
-LED = Pin(2, Pin.OUT)
+# Blue LED on pin 2, active low (inverted)
+LED = Signal(Pin(2, Pin.OUT), inverted=True)