Commit some sins in the name of "oh god oh god I don't really want to
be able to claim I know how the UART code works."

* Just return 115200 as the current baud rate. I should cache it in the
  device struct and return that but I'm lazy right now.
* don't error out on other ioctl settings for now, just silently ignore them.
* remove some code that was copied from the 8250 driver that isn't needed
  any longer.

Tested:

* AR9331, Carambola-2 board.