Restore the status quo before my last commit. Prior to it, sio took

Restore the status quo before my last commit.  Prior to it, sio took
precedence uart.  With my last change, it became a tie, and uart seems
to always win on my amd64.  This was not my intention, so have sio be
just a tiny bit more preferred than uart.

Note: I'm not making any judgement on the merits of uart winning.  I'm
just saying that if we want to change it, we do it on purpose.