fixed inconsistent spacing

[serge-m]

Trigger

On Upboard with ubuntu 16:

$ python
Python 3.5.2 (default, Nov 12 2018, 13:43:14) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import Adafruit_GPIO.I2C as I2C
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/up/work/blind/Adafruit_Python_GPIO/Adafruit_GPIO/I2C.py", line 56
    return 1
           ^

Changes

replaced tabs with spaces

[serge-m]

@nicola-lunghi would that be useful for anyone?