pata_atiixp: fix second channel support

PIO and MWDMA timings are never programmed for the second channel
because timing registers are treated as 16-bit long ones.

The bug is an attixp -> pata_atiixp regression and goes back to:

	commit 669a5db4
	Author: Jeff Garzik <jeff@garzik.org>
	Date:   Tue Aug 29 18:12:40 2006 -0400

	    [libata] Add a bunch of PATA drivers.

Cc: Krystian Juskowiak <jusko@tlen.pl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bbpetkov@yahoo.de>
Cc: Robert Hancock <hancockrwd@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>