Add bus_names/0 to porting guide; fix ref

Author: fhunleth

PORTING.md

@@ -41,6 +41,7 @@ The remain modifications should mostly be mechanical:
    collector will free unreferenced I2C references.
 7. If you manually implemented I2C bus retry logic, consider specifying the
    `:retries` option to have `Circuits.I2C` retry for you.
+8. Change calls to `ElixirALE.I2C.device_names/0` to `Circuits.I2C.bus_names/0`.
 
 If you find that you have to make any other changes, please let us know via an
 issue or PR so that other users can benefit.

lib/i2c.ex

@@ -34,7 +34,7 @@ defmodule Circuits.I2C do
   I2C bus names depend on the platform. Names are of the form "i2c-n" where the
   "n" is the bus number.  The correct bus number can be found in the
   documentation for the device or on a schematic. Another option is to call
-  `Circuits.I2C.bus_names/1` to list them for you.
+  `Circuits.I2C.bus_names/0` to list them for you.
 
   I2c buses may be opened more than once. There is no need to share an I2C bus
   reference between modules.