Tidy up / simplify "com" register initialization

[Jason Thorpe <thorpej%me.com@localhost>]

I'm working on an application where I need some additional run-time flexibility in how the "com" driver register map is setup.  COM_REGMAP cam do the job, but there is some untidiness around how com_regs is initialized.  This patch is a small step in cleaning that up, with some other minor changes to follow later.

This has been compiled-tested everywhere, and I will spot-check on a few different devices that I have handy.  Most of the changes are purely mechanical.

I'll commit in a couple of days unless there are serious objections.

Thx.

	https://www.dropbox.com/s/xl4y3jv2u68bnr2/com_regs-patch.txt

-- thorpej