atiixp: fix missing parentheses

Fix missing parentheses so PIO/DMA timings for master device on the
second channel are programmed correctly (IOW "8 0 24 16" offset values
should be used instead of the current "8 0 16 16").

[ The bug went unnoticed because after PIO/DMA timings get programmed
  incorrectly for the third device they are overwritten with timings
  for the fourth device and since BIOS should also program timings for
  the third device everything should work fine until suspend/resume
  cycle or user requested transfer mode changes. ]

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
[bart: update patch description]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>